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Title: Faraday As A Discoverer
Author: John Tyndall
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Preface to the fifth edition.

Daily and weekly, from all parts of the world, I receive publications
bearing upon the practical applications of electricity. This great
movement, the ultimate outcome of which is not to be foreseen, had its
origin in the discoveries made by Michael Faraday, sixty-two years ago.
From these discoveries have sprung applications of the telephone order,
together with various forms of the electric telegraph. From them have
sprung the extraordinary advances made in electrical illumination. Faraday
could have had but an imperfect notion of the expansions of which his
discoveries were capable. Still he had a vivid and strong imagination, and
I do not doubt that he saw possibilities which did not disclose themselves
to the general scientific mind. He knew that his discoveries had their
practical side, but he steadfastly resisted the seductions of this side,
applying himself to the development of principles; being well aware that
the practical question would receive due development hereafter.

During my sojourn in Switzerland this year, I read through the proofs of
this new edition, and by my reading was confirmed in the conviction that
the book ought not to be suffered to go out of print. The memoir was
written under great pressure, but I am not ashamed of it as it stands.
Glimpses of Faraday's character and gleams of his discoveries are there to
be found which will be of interest to humanity to the end of time.

John Tyndall. Hind Head, December, 1893.

[Note.—It was, I believe, my husband's intention to substitute this
Preface, written a few days before his death, for all former Prefaces. As,
however, he had not the opportunity of revising the old prefatory pages
himself, they have been allowed to remain just as they stood in the last
edition.

Louisa C. Tyndall.]

Preface to the fourth edition.

When consulted a short time ago as to the republication of 'Faraday as a
Discoverer,' it seemed to me that the labours, and points of character, of
so great a worker and so good a man should not be allowed to vanish from
the public eye. I therefore willingly fell in with the proposal of my
Publishers to issue a new edition of the little book.

Royal Institution, February, 1884.

Preface to the second edition.

The experimental researches of Faraday are so voluminous, their
descriptions are so detailed, and their wealth of illustration is so
great, as to render it a heavy labour to master them. The multiplication
of proofs, necessary and interesting when the new truths had to be
established, are however less needful now when these truths have become
household words in science. I have therefore tried in the following pages
to compress the body, without injury to the spirit, of these imperishable
investigations, and to present them in a form which should be convenient
and useful to the student of the present day.

While I write, the volumes of the Life of Faraday by Dr. Bence Jones have
reached my hands. To them the reader must refer for an account of
Faraday's private relations. A hasty glance at the work shows me that the
reverent devotion of the biographer has turned to admirable account the
materials at his command.

The work of Dr. Bence Jones enables me to correct a statement regarding
Wollaston's and Faraday's respective relations to the discovery of
Magnetic Rotation. Wollaston's idea was to make the wire carrying a
current rotate round its own axis: an idea afterwards realised by the
celebrated Ampere. Faraday's discovery was to make the wire carrying the
current revolve round the pole of a magnet and the reverse.

John Tyndall. Royal Institution: December, 1869.

FARADAY AS A DISCOVERER.

Chapter 1.

Parentage: introduction to the royal institution: earliest
experiments: first royal society paper: marriage.

It has been thought desirable to give you and the world some image of
MICHAEL FARADAY, as a scientific investigator and discoverer. The attempt
to respond to this desire has been to me a labour of difficulty, if also a
labour of love. For however well acquainted I may be with the researches
and discoveries of that great master—however numerous the
illustrations which occur to me of the loftiness of Faraday's character
and the beauty of his life—still to grasp him and his researches as
a whole; to seize upon the ideas which guided him, and connected them; to
gain entrance into that strong and active brain, and read from it the
riddle of the world—this is a work not easy of performance, and all
but impossible amid the distraction of duties of another kind. That I
should at one period or another speak to you regarding Faraday and his
work is natural, if not inevitable; but I did not expect to be called upon
to speak so soon. Still the bare suggestion that this is the fit and
proper time for speech sent me immediately to my task: from it I have
returned with such results as I could gather, and also with the wish that
those results were more worthy than they are of the greatness of my theme.

It is not my intention to lay before you a life of Faraday in the ordinary
acceptation of the term. The duty I have to perform is to give you some
notion of what he has done in the world; dwelling incidentally on the
spirit in which his work was executed, and introducing such personal
traits as may be necessary to the completion of your picture of the
philosopher, though by no means adequate to give you a complete idea of
the man.

The newspapers have already informed you that Michael Faraday was born at
Newington Butts, on September 22, 1791, and that he died at Hampton Court,
on August 25, 1867. Believing, as I do, in the general truth of the
doctrine of hereditary transmission—sharing the opinion of Mr.
Carlyle, that 'a really able man never proceeded from entirely stupid
parents'—I once used the privilege of my intimacy with Mr. Faraday
to ask him whether his parents showed any signs of unusual ability. He
could remember none. His father, I believe, was a great sufferer during
the latter years of his life, and this might have masked whatever
intellectual power he possessed. When thirteen years old, that is to say
in 1804, Faraday was apprenticed to a bookseller and bookbinder in
Blandford Street, Manchester Square: here he spent eight years of his
life, after which he worked as a journeyman elsewhere.

You have also heard the account of Faraday's first contact with the Royal
Institution; that he was introduced by one of the members to Sir Humphry
Davy's last lectures, that he took notes of those lectures; wrote them
fairly out, and sent them to Davy, entreating him at the same time to
enable him to quit trade, which he detested, and to pursue science, which
he loved. Davy was helpful to the young man, and this should never be
forgotten: he at once wrote to Faraday, and afterwards, when an
opportunity occurred, made him his assistant. (1) Mr. Gassiot has lately
favoured me with the following reminiscence of this time:—

'Clapham Common, Surrey,

'November 28, 1867.

'My Dear Tyndall,—Sir H. Davy was accustomed to call on the late Mr.
Pepys, in the Poultry, on his way to the London Institution, of which
Pepys was one of the original managers; the latter told me that on one
occasion Sir H. Davy, showing him a letter, said: "Pepys, what am I to do,
here is a letter from a young man named Faraday; he has been attending my
lectures, and wants me to give him employment at the Royal Institution—what
can I do?" "Do?" replied Pepys, "put him to wash bottles; if he is good
for anything he will do it directly, if he refuses he is good for
nothing." "No, no," replied Davy; "we must try him with something better
than that." The result was, that Davy engaged him to assist in the
Laboratory at weekly wages.

'Davy held the joint office of Professor of Chemistry and Director of the
Laboratory; he ultimately gave up the former to the late Professor Brande,
but he insisted that Faraday should be appointed Director of the
Laboratory, and, as Faraday told me, this enabled him on subsequent
occasions to hold a definite position in the Institution, in which he was
always supported by Davy. I believe he held that office to the last.

'Believe me, my dear Tyndall, yours truly,

'J. P. Gassiot.

'Dr. Tyndall.'

From a letter written by Faraday himself soon after his appointment as
Davy's assistant, I extract the following account of his introduction to
the Royal Institution:—

'London, Sept. 13, 1813.

'As for myself, I am absent (from home) nearly day and night, except
occasional calls, and it is likely shall shortly be absent entirely, but
this (having nothing more to say, and at the request of my mother) I will
explain to you. I was formerly a bookseller and binder, but am now turned
philosopher, (2) which happened thus:—Whilst an apprentice, I, for
amusement, learnt a little chemistry and other parts of philosophy, and
felt an eager desire to proceed in that way further. After being a
journeyman for six months, under a disagreeable master, I gave up my
business, and through the interest of a Sir H. Davy, filled the situation
of chemical assistant to the Royal Institution of Great Britain, in which
office I now remain; and where I am constantly employed in observing the
works of nature, and tracing the manner in which she directs the order and
arrangement of the world. I have lately had proposals made to me by Sir
Humphry Davy to accompany him in his travels through Europe and Asia, as
philosophical assistant. If I go at all I expect it will be in October
next—about the end; and my absence from home will perhaps be as long
as three years. But as yet all is uncertain.'

This account is supplemented by the following letter, written by Faraday
to his friend De la Rive, (3) on the occasion of the death of Mrs. Marcet.
The letter is dated September 2, 1858:—

'My Dear Friend,—Your subject interested me deeply every way; for
Mrs. Marcet was a good friend to me, as she must have been to many of the
human race. I entered the shop of a bookseller and bookbinder at the age
of thirteen, in the year 1804, remained there eight years, and during the
chief part of my time bound books. Now it was in those books, in the hours
after work, that I found the beginning of my philosophy.

There were two that especially helped me, the "Encyclopaedia Britannica,"
from which I gained my first notions of electricity, and Mrs. Marcet's
"Conversation on Chemistry," which gave me my foundation in that science.

'Do not suppose that I was a very deep thinker, or was marked as a
precocious person. I was a very lively imaginative person, and could
believe in the "Arabian Nights" as easily as in the "Encyclopaedia." But
facts were important to me, and saved me. I could trust a fact, and always
cross-examined an assertion. So when I questioned Mrs. Marcet's book by
such little experiments as I could find means to perform, and found it
true to the facts as I could understand them, I felt that I had got hold
of an anchor in chemical knowledge, and clung fast to it. Thence my deep
veneration for Mrs. Marcet—first as one who had conferred great
personal good and pleasure on me; and then as one able to convey the truth
and principle of those boundless fields of knowledge which concern natural
things to the young, untaught, and inquiring mind.

'You may imagine my delight when I came to know Mrs. Marcet personally;
how often I cast my thoughts backward, delighting to connect the past and
the present; how often, when sending a paper to her as a thank-offering, I
thought of my first instructress, and such like thoughts will remain with
me.

'I have some such thoughts even as regards your own father; who was, I may
say, the first who personally at Geneva, and afterwards by correspondence,
encouraged, and by that sustained me.'

Twelve or thirteen years ago Mr. Faraday and myself quitted the
Institution one evening together, to pay a visit to our friend Grove in
Baker Street. He took my arm at the door, and, pressing it to his side in
his warm genial way, said, 'Come, Tyndall, I will now show you something
that will interest you.' We walked northwards, passed the house of Mr.
Babbage, which drew forth a reference to the famous evening parties once
assembled there. We reached Blandford Street, and after a little looking
about he paused before a stationer's shop, and then went in. On entering
the shop, his usual animation seemed doubled; he looked rapidly at
everything it contained. To the left on entering was a door, through which
he looked down into a little room, with a window in front facing Blandford
Street. Drawing me towards him, he said eagerly, 'Look there, Tyndall,
that was my working-place. I bound books in that little nook.' A
respectable-looking woman stood behind the counter: his conversation with
me was too low to be heard by her, and he now turned to the counter to buy
some cards as an excuse for our being there. He asked the woman her name—her
predecessor's name—his predecessor's name. 'That won't do,' he said,
with good-humoured impatience; 'who was his predecessor?' 'Mr. Riebau,'
she replied, and immediately added, as if suddenly recollecting herself,
'He, sir, was the master of Sir Charles Faraday.' 'Nonsense!' he
responded, 'there is no such person.' Great was her delight when I told
her the name of her visitor; but she assured me that as soon as she saw
him running about the shop, she felt-though she did not know why—that
it must be 'Sir Charles Faraday.'

Faraday did, as you know, accompany Davy to Rome: he was re-engaged by the
managers of the Royal Institution on May 15, 1815. Here he made rapid
progress in chemistry, and after a time was entrusted with easy analyses
by Davy. In those days the Royal Institution published 'The Quarterly
Journal of Science,' the precursor of our own 'Proceedings.' Faraday's
first contribution to science appeared in that journal in 1816. It was an
analysis of some caustic lime from Tuscany, which had been sent to Davy by
the Duchess of Montrose. Between this period and 1818 various notes and
short papers were published by Faraday. In 1818 he experimented upon
'Sounding Flames.' Professor Auguste De la Rive had investigated those
sounding flames, and had applied to them an explanation which completely
accounted for a class of sounds discovered by himself, but did not account
for those known to his predecessors. By a few simple and conclusive
experiments, Faraday proved the explanation insufficient. It is an epoch
in the life of a young man when he finds himself correcting a person of
eminence, and in Faraday's case, where its effect was to develop a modest
self-trust, such an event could not fail to act profitably.

From time to time between 1818 and 1820 Faraday published scientific notes
and notices of minor weight. At this time he was acquiring, not producing;
working hard for his master and storing and strengthening his own mind. He
assisted Mr. Brande in his lectures, and so quietly, skilfully, and
modestly was his work done, that Mr. Brande's vocation at the time was
pronounced 'lecturing on velvet.' In 1820 Faraday published a chemical
paper 'on two new compounds of chlorine and carbon, and on a new compound
of iodine, carbon, and hydrogen.' This paper was read before the Royal
Society on December 21, 1820, and it was the first of his that was
honoured with a place in the 'Philosophical Transactions.'

On June 12, 1821, he married, and obtained leave to bring his young wife
into his rooms at the Royal Institution. There for forty-six years they
lived together, occupying the suite of apartments which had been
previously in the successive occupancy of Young, Davy, and Brande. At the
time of her marriage Mrs. Faraday was twenty-one years of age, he being
nearly thirty. Regarding this marriage I will at present limit myself to
quoting an entry written in Faraday's own hand in his book of diplomas,
which caught my eye while in his company some years ago. It ran thus:—

'25th January, 1847. 'Amongst these records and events, I here insert the
date of one which, as a source of honour and happiness, far exceeds all
the rest. We were married on June 12, 1821.

'M. Faraday.'

Then follows the copy of the minutes, dated May 21, 1821, which gave him
additional rooms, and thus enabled him to bring his wife to the Royal
Institution. A feature of Faraday's character which I have often noticed
makes itself apparent in this entry. In his relations to his wife he added
chivalry to affection.

Footnotes to Chapter 1

(1) Here is Davy's recommendation of Faraday, presented to
the managers of the Royal Institution, at a meeting on the
18th of March, 1813, Charles Hatchett, Esq., in the chair:—
'Sir Humphry Davy has the honour to inform the managers that
he has found a person who is desirous to occupy the
situation in the Institution lately filled by William Payne.
His name is Michael Faraday. He is a youth of twenty-two
years of age. As far as Sir H. Davy has been able to
observe or ascertain, he appears well fitted for the
situation. His habits seem good; his disposition active and
cheerful, and his manner intelligent. He is willing to
engage himself on the same terms as given to Mr. Payne at
the time of quitting the Institution.
'Resolved,—That Michael Faraday be engaged to fill the
situation lately occupied by Mr. Payne, on the same terms.'
(2) Faraday loved this word and employed it to the last; he
had an intense dislike to the modern term physicist.
(3) To whom I am indebted for a copy of the original letter.

Chapter 2.

Oersted, in 1820, discovered the action of a voltaic current on a magnetic
needle; and immediately afterwards the splendid intellect of Ampere
succeeded in showing that every magnetic phenomenon then known might be
reduced to the mutual action of electric currents. The subject occupied
all men's thoughts: and in this country Dr. Wollaston sought to convert
the deflection of the needle by the current into a permanent rotation of
the needle round the current. He also hoped to produce the reciprocal
effect of causing a current to rotate round a magnet. In the early part of
1821, Wollaston attempted to realise this idea in the presence of Sir
Humphry Davy in the laboratory of the Royal Institution. (1) This was well
calculated to attract Faraday's attention to the subject. He read much
about it; and in the months of July, August, and September he wrote a
'history of the progress of electro-magnetism,' which he published in
Thomson's 'Annals of Philosophy.' Soon afterwards he took up the subject
of 'Magnetic Rotations,' and on the morning of Christmas-day, 1821, he
called his wife to witness, for the first time, the revolution of a
magnetic needle round an electric current. Incidental to the 'historic
sketch,' he repeated almost all the experiments there referred to; and
these, added to his own subsequent work, made him practical master of all
that was then known regarding the voltaic current. In 1821, he also
touched upon a subject which subsequently received his closer attention—the
vaporization of mercury at common temperatures; and immediately afterwards
conducted, in company with Mr. Stodart, experiments on the alloys of
steel. He was accustomed in after years to present to his friends razors
formed from one of the alloys then discovered.

During Faraday's hours of liberty from other duties, he took up subjects
of inquiry for himself; and in the spring of 1823, thus self-prompted, he
began the examination of a substance which had long been regarded as the
chemical element chlorine, in a solid form, but which Sir Humphry Davy, in
1810, had proved to be a hydrate of chlorine, that is, a compound of
chlorine and water. Faraday first analysed this hydrate, and wrote out an
account of its composition. This account was looked over by Davy, who
suggested the heating of the hydrate under pressure in a sealed glass
tube. This was done. The hydrate fused at a blood-heat, the tube became
filled with a yellow atmosphere, and was afterwards found to contain two
liquid substances. Dr. Paris happened to enter the laboratory while
Faraday was at work. Seeing the oily liquid in his tube, he rallied the
young chemist for his carelessness in employing soiled vessels. On filing
off the end of the tube, its contents exploded and the oily matter
vanished. Early next morning, Dr. Paris received the following note:—

'Dear Sir,—The oil you noticed yesterday turns out to be liquid
chlorine.

'Yours faithfully,

'M. Faraday.' (2)

The gas had been liquefied by its own pressure. Faraday then tried
compression with a syringe, and succeeded thus in liquefying the gas.

To the published account of this experiment Davy added the following note:—'In
desiring Mr. Faraday to expose the hydrate of chlorine in a closed glass
tube, it occurred to me that one of three things would happen: that
decomposition of water would occur;... or that the chlorine would separate
in a fluid state.' Davy, moreover, immediately applied the method of
self-compressing atmosphere to the liquefaction of muriatic gas. Faraday
continued the experiments, and succeeded in reducing a number of gases
till then deemed permanent to the liquid condition. In 1844 he returned to
the subject, and considerably expanded its limits. These important
investigations established the fact that gases are but the vapours of
liquids possessing a very low boiling-point, and gave a sure basis to our
views of molecular aggregation. The account of the first investigation was
read before the Royal Society on April 10, 1823, and was published, in
Faraday's name, in the 'Philosophical Transactions.' The second memoir was
sent to the Royal Society on December 19, 1844. I may add that while he
was conducting his first experiments on the liquefaction of gases,
thirteen pieces of glass were on one occasion driven by an explosion into
Faraday's eye.

Some small notices and papers, including the observation that glass
readily changes colour in sunlight, follow here. In 1825 and 1826 Faraday
published papers in the 'Philosophical Transactions' on 'new compounds of
carbon and hydrogen,' and on 'sulphonaphthalic acid.' In the former of
these papers he announced the discovery of Benzol, which, in the hands of
modern chemists, has become the foundation of our splendid aniline dyes.
But he swerved incessantly from chemistry into physics; and in 1826 we
find him engaged in investigating the limits of vaporization, and showing,
by exceedingly strong and apparently conclusive arguments, that even in
the case of mercury such a limit exists; much more he conceived it to be
certain that our atmosphere does not contain the vapour of the fixed
constituents of the earth's crust. This question, I may say, is likely to
remain an open one. Dr. Rankine, for example, has lately drawn attention
to the odour of certain metals; whence comes this odour, if it be not from
the vapour of the metal?

In 1825 Faraday became a member of a committee, to which Sir John Herschel
and Mr. Dollond also belonged, appointed by the Royal Society to examine,
and if possible improve, the manufacture of glass for optical purposes.
Their experiments continued till 1829, when the account of them
constituted the subject of a 'Bakerian Lecture.' This lectureship, founded
in 1774 by Henry Baker, Esq., of the Strand, London, provides that every
year a lecture shall be given before the Royal Society, the sum of four
pounds being paid to the lecturer. The Bakerian Lecture, however, has long
since passed from the region of pay to that of honour, papers of mark only
being chosen for it by the council of the Society. Faraday's first
Bakerian Lecture, 'On the Manufacture of Glass for Optical Purposes,' was
delivered at the close of 1829. It is a most elaborate and conscientious
description of processes, precautions, and results: the details were so
exact and so minute, and the paper consequently so long, that three
successive sittings of the Royal Society were taken up by the delivery of
the lecture. (3) This glass did not turn out to be of important practical
use, but it happened afterwards to be the foundation of two of Faraday's
greatest discoveries. (4)

The experiments here referred to were commenced at the Falcon Glass Works,
on the premises of Messrs. Green and Pellatt, but Faraday could not
conveniently attend to them there. In 1827, therefore, a furnace was
erected in the yard of the Royal Institution; and it was at this time, and
with a view of assisting him at the furnace, that Faraday engaged Sergeant
Anderson, of the Royal Artillery, the respectable, truthful, and
altogether trustworthy man whose appearance here is so fresh in our
memories. Anderson continued to be the reverential helper of Faraday and
the faithful servant of this Institution for nearly forty years. (5)

In 1831 Faraday published a paper, 'On a peculiar class of Optical
Deceptions,' to which I believe the beautiful optical toy called the
Chromatrope owes its origin. In the same year he published a paper on
Vibrating Surfaces, in which he solved an acoustical problem which, though
of extreme simplicity when solved, appears to have baffled many eminent
men. The problem was to account for the fact that light bodies, such as
the seed of lycopodium, collected at the vibrating parts of sounding
plates, while sand ran to the nodal lines. Faraday showed that the light
bodies were entangled in the little whirlwinds formed in the air over the
places of vibration, and through which the heavier sand was readily
projected. Faraday's resources as an experimentalist were so wonderful,
and his delight in experiment was so great, that he sometimes almost ran
into excess in this direction. I have heard him say that this paper on
vibrating surfaces was too heavily laden with experiments.

Footnotes to Chapter 2

(1) The reader's attention is directed to the concluding
paragraph of the 'Preface to the Second Edition written in
December, 1869. Also to the Life of Faraday by Dr. Bence
Jones, vol. i. p. 338 et seq.
(2) Paris: Life of Davy, p. 391.
(3) Viz., November 19, December 3 and 10.
(4) I make the following extract from a letter from Sir John
Herschel, written to me from Collingwood, on the 3rd of
November, 1867:—'I will take this opportunity to mention
that I believe myself to have originated the suggestion of
the employment of borate of lead for optical purposes. It
was somewhere in the year 1822, as well as I can recollect,
that I mentioned it to Sir James (then Mr.) South; and, in
consequence, the trial was made in his laboratory in
Blackman Street, by precipitating and working a large
quantity of borate of lead, and fusing it under a muffle in
a porcelain evaporating dish. A very limpid (though
slightly yellow) glass resulted, the refractive index 1.866!
(which you will find set down in my table of refractive
indices in my article "Light," Encyclopaedia Metropolitana).
It was, however, too soft for optical use as an object-
glass. This Faraday overcame, at least to a considerable
degree, by the introduction of silica.'
(5) Regarding Anderson, Faraday writes thus in 1845:—'I
cannot resist the occasion that is thus offered to me of
mentioning the name of Mr. Anderson, who came to me as an
assistant in the glass experiments, and has remained ever
since in the laboratory of the Royal Institution. He
assisted me in all the researches into which I have entered
since that time; and to his care, steadiness, exactitude,
and faithfulness in the performance of all that has been
committed to his charge, I am much indebted.—M. F.' (Exp.
Researches, vol. iii. p. 3, footnote.)

Chapter 3.

The work thus referred to, though sufficient of itself to secure no mean
scientific reputation, forms but the vestibule of Faraday's achievements.
He had been engaged within these walls for eighteen years. During part of
the time he had drunk in knowledge from Davy, and during the remainder he
continually exercised his capacity for independent inquiry. In 1831 we
have him at the climax of his intellectual strength, forty years of age,
stored with knowledge and full of original power. Through reading,
lecturing, and experimenting, he had become thoroughly familiar with
electrical science: he saw where light was needed and expansion possible.
The phenomena of ordinary electric induction belonged, as it were, to the
alphabet of his knowledge: he knew that under ordinary circumstances the
presence of an electrified body was sufficient to excite, by induction, an
unelectrified body. He knew that the wire which carried an electric
current was an electrified body, and still that all attempts had failed to
make it excite in other wires a state similar to its own.

What was the reason of this failure? Faraday never could work from the
experiments of others, however clearly described. He knew well that from
every experiment issues a kind of radiation, luminous in different degrees
to different minds, and he hardly trusted himself to reason upon an
experiment that he had not seen. In the autumn of 1831 he began to repeat
the experiments with electric currents, which, up to that time, had
produced no positive result. And here, for the sake of younger inquirers,
if not for the sake of us all, it is worth while to dwell for a moment on
a power which Faraday possessed in an extraordinary degree. He united vast
strength with perfect flexibility. His momentum was that of a river, which
combines weight and directness with the ability to yield to the flexures
of its bed. The intentness of his vision in any direction did not
apparently diminish his power of perception in other directions; and when
he attacked a subject, expecting results he had the faculty of keeping his
mind alert, so that results different from those which he expected should
not escape him through preoccupation.

He began his experiments 'on the induction of electric currents' by
composing a helix of two insulated wires which were wound side by side
round the same wooden cylinder. One of these wires he connected with a
voltaic battery of ten cells, and the other with a sensitive galvanometer.
When connection with the battery was made, and while the current flowed,
no effect whatever was observed at the galvanometer. But he never accepted
an experimental result, until he had applied to it the utmost power at his
command. He raised his battery from 10 cells to 120 cells, but without
avail. The current flowed calmly through the battery wire without
producing, during its flow, any sensible result upon the galvanometer.

'During its flow,' and this was the time when an effect was expected—but
here Faraday's power of lateral vision, separating, as it were, from the
line of expectation, came into play—he noticed that a feeble
movement of the needle always occurred at the moment when he made contact
with the battery; that the needle would afterwards return to its former
position and remain quietly there unaffected by the flowing current. At
the moment, however, when the circuit was interrupted the needle again
moved, and in a direction opposed to that observed on the completion of
the circuit.

This result, and others of a similar kind, led him to the conclusion 'that
the battery current through the one wire did in reality induce a similar
current through the other; but that it continued for an instant only, and
partook more of the nature of the electric wave from a common Leyden jar
than of the current from a voltaic battery.' The momentary currents thus
generated were called induced currents, while the current which generated
them was called the inducing current. It was immediately proved that the
current generated at making the circuit was always opposed in direction to
its generator, while that developed on the rupture of the circuit
coincided in direction with the inducing current. It appeared as if the
current on its first rush through the primary wire sought a purchase in
the secondary one, and, by a kind of kick, impelled backward through the
latter an electric wave, which subsided as soon as the primary current was
fully established.

Faraday, for a time, believed that the secondary wire, though quiescent
when the primary current had been once established, was not in its natural
condition, its return to that condition being declared by the current
observed at breaking the circuit. He called this hypothetical state of the
wire the electro-tonic state: he afterwards abandoned this hypothesis, but
seemed to return to it in later life. The term electro-tonic is also
preserved by Professor Du Bois Reymond to express a certain electric
condition of the nerves, and Professor Clerk Maxwell has ably defined and
illustrated the hypothesis in the Tenth Volume of the 'Transactions of the
Cambridge Philosophical Society.'

The mere approach of a wire forming a closed curve to a second wire
through which a voltaic current flowed was then shown by Faraday to be
sufficient to arouse in the neutral wire an induced current, opposed in
direction to the inducing current; the withdrawal of the wire also
generated a current having the same direction as the inducing current;
those currents existed only during the time of approach or withdrawal, and
when neither the primary nor the secondary wire was in motion, no matter
how close their proximity might be, no induced current was generated.

Faraday has been called a purely inductive philosopher. A great deal of
nonsense is, I fear, uttered in this land of England about induction and
deduction. Some profess to befriend the one, some the other, while the
real vocation of an investigator, like Faraday, consists in the incessant
marriage of both. He was at this time full of the theory of Ampere, and it
cannot be doubted that numbers of his experiments were executed merely to
test his deductions from that theory. Starting from the discovery of
Oersted, the illustrious French philosopher had shown that all the
phenomena of magnetism then known might be reduced to the mutual
attractions and repulsions of electric currents. Magnetism had been
produced from electricity, and Faraday, who all his life long entertained
a strong belief in such reciprocal actions, now attempted to effect the
evolution of electricity from magnetism. Round a welded iron ring he
placed two distinct coils of covered wire, causing the coils to occupy
opposite halves of the ring. Connecting the ends of one of the coils with
a galvanometer, he found that the moment the ring was magnetised, by
sending a current through the other coil, the galvanometer needle whirled
round four or five times in succession. The action, as before, was that of
a pulse, which vanished immediately. On interrupting the circuit, a whirl
of the needle in the opposite direction occurred. It was only during the
time of magnetization or demagnetization that these effects were produced.
The induced currents declared a change of condition only, and they
vanished the moment the act of magnetization or demagnetization was
complete.

The effects obtained with the welded ring were also obtained with straight
bars of iron. Whether the bars were magnetised by the electric current, or
were excited by the contact of permanent steel magnets, induced currents
were always generated during the rise, and during the subsidence of the
magnetism. The use of iron was then abandoned, and the same effects were
obtained by merely thrusting a permanent steel magnet into a coil of wire.
A rush of electricity through the coil accompanied the insertion of the
magnet; an equal rush in the opposite direction accompanied its
withdrawal. The precision with which Faraday describes these results, and
the completeness with which he defines the boundaries of his facts, are
wonderful. The magnet, for example, must not be passed quite through the
coil, but only half through; for if passed wholly through, the needle is
stopped as by a blow, and then he shows how this blow results from a
reversal of the electric wave in the helix. He next operated with the
powerful permanent magnet of the Royal Society, and obtained with it, in
an exalted degree, all the foregoing phenomena.

And now he turned the light of these discoveries upon the darkest physical
phenomenon of that day. Arago had discovered, in 1824, that a disk of
non-magnetic metal had the power of bringing a vibrating magnetic needle
suspended over it rapidly to rest; and that on causing the disk to rotate
the magnetic needle rotated along with it. When both were quiescent, there
was not the slightest measurable attraction or repulsion exerted between
the needle and the disk; still when in motion the disk was competent to
drag after it, not only a light needle, but a heavy magnet. The question
had been probed and investigated with admirable skill both by Arago and
Ampere, and Poisson had published a theoretic memoir on the subject; but
no cause could be assigned for so extraordinary an action. It had also
been examined in this country by two celebrated men, Mr. Babbage and Sir
John Herschel; but it still remained a mystery. Faraday always recommended
the suspension of judgment in cases of doubt. 'I have always admired,' he
says, 'the prudence and philosophical reserve shown by M. Arago in
resisting the temptation to give a theory of the effect he had discovered,
so long as he could not devise one which was perfect in its application,
and in refusing to assent to the imperfect theories of others.' Now,
however, the time for theory had come. Faraday saw mentally the rotating
disk, under the operation of the magnet, flooded with his induced
currents, and from the known laws of interaction between currents and
magnets he hoped to deduce the motion observed by Arago. That hope he
realised, showing by actual experiment that when his disk rotated currents
passed through it, their position and direction being such as must, in
accordance with the established laws of electro-magnetic action, produce
the observed rotation.

Introducing the edge of his disk between the poles of the large horseshoe
magnet of the Royal Society, and connecting the axis and the edge of the
disk, each by a wire with a galvanometer, he obtained, when the disk was
turned round, a constant flow of electricity. The direction of the current
was determined by the direction of the motion, the current being reversed
when the rotation was reversed. He now states the law which rules the
production of currents in both disks and wires, and in so doing uses, for
the first time, a phrase which has since become famous. When iron filings
are scattered over a magnet, the particles of iron arrange themselves in
certain determinate lines called magnetic curves. In 1831, Faraday for the
first time called these curves 'lines of magnetic force'; and he showed
that to produce induced currents neither approach to nor withdrawal from a
magnetic source, or centre, or pole, was essential, but that it was only
necessary to cut appropriately the lines of magnetic force. Faraday's
first paper on Magneto-electric Induction, which I have here endeavoured
to condense, was read before the Royal Society on the 24th of November,
1831.

On January 12, 1832, he communicated to the Royal Society a second paper
on Terrestrial Magneto-electric Induction, which was chosen as the
Bakerian Lecture for the year. He placed a bar of iron in a coil of wire,
and lifting the bar into the direction of the dipping needle, he excited
by this action a current in the coil. On reversing the bar, a current in
the opposite direction rushed through the wire. The same effect was
produced when, on holding the helix in the line of dip, a bar of iron was
thrust into it. Here, however, the earth acted on the coil through the
intermediation of the bar of iron. He abandoned the bar and simply set a
copper plate spinning in a horizontal plane; he knew that the earth's
lines of magnetic force then crossed the plate at an angle of about
70degrees. When the plate spun round, the lines of force were intersected
and induced currents generated, which produced their proper effect when
carried from the plate to the galvanometer. 'When the plate was in the
magnetic meridian, or in any other plane coinciding with the magnetic dip,
then its rotation produced no effect upon the galvanometer.'

At the suggestion of a mind fruitful in suggestions of a profound and
philosophic character—I mean that of Sir John Herschel—Mr.
Barlow, of Woolwich, had experimented with a rotating iron shell. Mr.
Christie had also performed an elaborate series of experiments on a
rotating iron disk. Both of them had found that when in rotation the body
exercised a peculiar action upon the magnetic needle, deflecting it in a
manner which was not observed during quiescence; but neither of them was
aware at the time of the agent which produced this extraordinary
deflection. They ascribed it to some change in the magnetism of the iron
shell and disk.

But Faraday at once saw that his induced currents must come into play
here, and he immediately obtained them from an iron disk. With a hollow
brass ball, moreover, he produced the effects obtained by Mr. Barlow. Iron
was in no way necessary: the only condition of success was that the
rotating body should be of a character to admit of the formation of
currents in its substance: it must, in other words, be a conductor of
electricity. The higher the conducting power the more copious were the
currents. He now passes from his little brass globe to the globe of the
earth. He plays like a magician with the earth's magnetism. He sees the
invisible lines along which its magnetic action is exerted, and sweeping
his wand across these lines evokes this new power. Placing a simple loop
of wire round a magnetic needle he bends its upper portion to the west:
the north pole of the needle immediately swerves to the east: he bends his
loop to the east, and the north pole moves to the west. Suspending a
common bar magnet in a vertical position, he causes it to spin round its
own axis. Its pole being connected with one end of a galvanometer wire,
and its equator with the other end, electricity rushes round the
galvanometer from the rotating magnet. He remarks upon the 'singular
independence' of the magnetism and the body of the magnet which carries
it. The steel behaves as if it were isolated from its own magnetism.

And then his thoughts suddenly widen, and he asks himself whether the
rotating earth does not generate induced currents as it turns round its
axis from west to east. In his experiment with the twirling magnet the
galvanometer wire remained at rest; one portion of the circuit was in
motion relatively to another portion. But in the case of the twirling
planet the galvanometer wire would necessarily be carried along with the
earth; there would be no relative motion. What must be the consequence?
Take the case of a telegraph wire with its two terminal plates dipped into
the earth, and suppose the wire to lie in the magnetic meridian. The
ground underneath the wire is influenced like the wire itself by the
earth's rotation; if a current from south to north be generated in the
wire, a similar current from south to north would be generated in the
earth under the wire; these currents would run against the same terminal
plate, and thus neutralise each other.

This inference appears inevitable, but his profound vision perceived its
possible invalidity. He saw that it was at least possible that the
difference of conducting power between the earth and the wire might give
one an advantage over the other, and that thus a residual or differential
current might be obtained. He combined wires of different materials, and
caused them to act in opposition to each other, but found the combination
ineffectual. The more copious flow in the better conductor was exactly
counterbalanced by the resistance of the worse. Still, though experiment
was thus emphatic, he would clear his mind of all discomfort by operating
on the earth itself. He went to the round lake near Kensington Palace, and
stretched 480 feet of copper wire, north and south, over the lake, causing
plates soldered to the wire at its ends to dip into the water. The copper
wire was severed at the middle, and the severed ends connected with a
galvanometer. No effect whatever was observed. But though quiescent water
gave no effect, moving water might. He therefore worked at London Bridge
for three days during the ebb and flow of the tide, but without any
satisfactory result. Still he urges, 'Theoretically it seems a necessary
consequence, that where water is flowing there electric currents should be
formed. If a line be imagined passing from Dover to Calais through the
sea, and returning through the land, beneath the water, to Dover, it
traces out a circuit of conducting matter one part of which, when the
water moves up or down the channel, is cutting the magnetic curves of the
earth, whilst the other is relatively at rest.... There is every reason to
believe that currents do run in the general direction of the circuit
described, either one way or the other, according as the passage of the
waters is up or down the channel.' This was written before the submarine
cable was thought of, and he once informed me that actual observation upon
that cable had been found to be in accordance with his theoretic
deduction. (1)

Three years subsequent to the publication of these researches—that
is to say, on January 29, 1835—Faraday read before the Royal Society
a paper 'On the influence by induction of an electric current upon
itself.' A shock and spark of a peculiar character had been observed by a
young man named William Jenkin, who must have been a youth of some
scientific promise, but who, as Faraday once informed me, was dissuaded by
his own father from having anything to do with science. The investigation
of the fact noticed by Mr. Jenkin led Faraday to the discovery of the
extra current, or the current induced in the primary wire itself at the
moments of making and breaking contact, the phenomena of which he
described and illustrated in the beautiful and exhaustive paper referred
to.

Seven-and-thirty years have passed since the discovery of
magneto-electricity; but, if we except the extra current, until quite
recently nothing of moment was added to the subject. Faraday entertained
the opinion that the discoverer of a great law or principle had a right to
the 'spoils'—this was his term—arising from its illustration;
and guided by the principle he had discovered, his wonderful mind, aided
by his wonderful ten fingers, overran in a single autumn this vast domain,
and hardly left behind him the shred of a fact to be gathered by his
successors.

And here the question may arise in some minds, What is the use of it all?
The answer is, that if man's intellectual nature thirsts for knowledge,
then knowledge is useful because it satisfies this thirst. If you demand
practical ends, you must, I think, expand your definition of the term
practical, and make it include all that elevates and enlightens the
intellect, as well as all that ministers to the bodily health and comfort
of men. Still, if needed, an answer of another kind might be given to the
question 'What is its use?' As far as electricity has been applied for
medical purposes, it has been almost exclusively Faraday's electricity.
You have noticed those lines of wire which cross the streets of London. It
is Faraday's currents that speed from place to place through these wires.
Approaching the point of Dungeness, the mariner sees an unusually
brilliant light, and from the noble phares of La Heve the same light
flashes across the sea. These are Faraday's sparks exalted by suitable
machinery to sunlike splendour. At the present moment the Board of Trade
and the Brethren of the Trinity House, as well as the Commissioners of
Northern Lights, are contemplating the introduction of the
Magneto-electric Light at numerous points upon our coasts; and future
generations will be able to refer to those guiding stars in answer to the
question. What has been the practical use of the labours of Faraday? But I
would again emphatically say, that his work needs no such justification,
and that if he had allowed his vision to be disturbed by considerations
regarding the practical use of his discoveries, those discoveries would
never have been made by him. 'I have rather,' he writes in 1831, 'been
desirous of discovering new facts and new relations dependent on
magneto-electric induction, than of exalting the force of those already
obtained; being assured that the latter would find their full development
hereafter.'

In 1817, when lecturing before a private society in London on the element
chlorine, Faraday thus expressed himself with reference to this question
of utility. 'Before leaving this subject, I will point out the history of
this substance, as an answer to those who are in the habit of saying to
every new fact. "What is its use?" Dr. Franklin says to such, "What is the
use of an infant?" The answer of the experimentalist is, "Endeavour to
make it useful." When Scheele discovered this substance, it appeared to
have no use; it was in its infancy and useless state, but having grown up
to maturity, witness its powers, and see what endeavours to make it useful
have done.'

Footnote to Chapter 3

(1) I am indebted to a friend for the following exquisite
morsel:—'A short time after the publication of Faraday's
first researches in magneto-electricity, he attended the
meeting of the British Association at Oxford, in 1832. On
this occasion he was requested by some of the authorities to
repeat the celebrated experiment of eliciting a spark from a
magnet, employing for this purpose the large magnet in the
Ashmolean Museum. To this he consented, and a large party
assembled to witness the experiments, which, I need not say,
were perfectly successful. Whilst he was repeating them a
dignitary of the University entered the room, and addressing
himself to Professor Daniell, who was standing near Faraday,
inquired what was going on. The Professor explained to him
as popularly as possible this striking result of Faraday's
great discovery. The Dean listened with attention and looked
earnestly at the brilliant spark, but a moment after he
assumed a serious countenance and shook his head; "I am
sorry for it," said he, as he walked away; in the middle of
the room he stopped for a moment and repeated, "I am sorry
for it:" then walking towards the door, when the handle was
in his hand he turned round and said, "Indeed I am sorry for
it; it is putting new arms into the hands of the
incendiary." This occurred a short time after the papers
had been filled with the doings of the hayrick burners. An
erroneous statement of what fell from the Dean's mouth was
printed at the time in one of the Oxford papers. He is there
wrongly stated to have said, "It is putting new arms into
the hands of the infidel."'

Chapter 4.

Points of Character.

A point highly illustrative of the character of Faraday now comes into
view. He gave an account of his discovery of Magneto-electricity in a
letter to his friend M. Hachette, of Paris, who communicated the letter to
the Academy of Sciences. The letter was translated and published; and
immediately afterwards two distinguished Italian philosophers took up the
subject, made numerous experiments, and published their results before the
complete memoirs of Faraday had met the public eye. This evidently
irritated him. He reprinted the paper of the learned Italians in the
'Philosophical Magazine,' accompanied by sharp critical notes from
himself. He also wrote a letter dated Dec. 1, 1832, to Gay Lussac, who was
then one of the editors of the 'Annales de Chimie,' in which he analysed
the results of the Italian philosophers, pointing out their errors, and
defending himself from what he regarded as imputations on his character.
The style of this letter is unexceptionable, for Faraday could not write
otherwise than as a gentleman; but the letter shows that had he willed it
he could have hit hard. We have heard much of Faraday's gentleness and
sweetness and tenderness. It is all true, but it is very incomplete. You
cannot resolve a powerful nature into these elements, and Faraday's
character would have been less admirable than it was had it not embraced
forces and tendencies to which the silky adjectives 'gentle' and 'tender'
would by no means apply. Underneath his sweetness and gentleness was the
heat of a volcano. He was a man of excitable and fiery nature; but through
high self-discipline he had converted the fire into a central glow and
motive power of life, instead of permitting it to waste itself in useless
passion. 'He that is slow to anger,' saith the sage, 'is greater than the
mighty, and he that ruleth his own spirit than he that taketh a city.'
Faraday was not slow to anger, but he completely ruled his own spirit, and
thus, though he took no cities, he captivated all hearts.

As already intimated, Faraday had contributed many of his minor papers—including
his first analysis of caustic lime—to the 'Quarterly Journal of
Science.' In 1832, he collected those papers and others together in a
small octavo volume, labelled them, and prefaced them thus:—

'Papers of mine, published in octavo, in the "Quarterly Journal of
Science," and elsewhere, since the time that Sir H. Davy encouraged me to
write the analysis of caustic lime.

'Some, I think (at this date), are good; others moderate; and some bad.
But I have put all into the volume, because of the utility they have been
of to me—and none more than the bad—in pointing out to me in
future, or rather, after times, the faults it became me to watch and to
avoid.

'As I never looked over one of my papers a year after it was written
without believing both in philosophy and manner it could have been much
better done, I still hope the collection may be of great use to me.

'M. Faraday.

'Aug. 18, 1832.'

'None more than the bad!' This is a bit of Faraday's innermost nature; and
as I read these words I am almost constrained to retract what I have said
regarding the fire and excitability of his character. But is he not all
the more admirable, through his ability to tone down and subdue that fire
and that excitability, so as to render himself able to write thus as a
little child? I once took the liberty of censuring the conclusion of a
letter of his to the Dean of St. Paul's. He subscribed himself 'humbly
yours,' and I objected to the adverb. 'Well, but, Tyndall,' he said, 'I am
humble; and still it would be a great mistake to think that I am not also
proud.' This duality ran through his character. A democrat in his defiance
of all authority which unfairly limited his freedom of thought, and still
ready to stoop in reverence to all that was really worthy of reverence, in
the customs of the world or the characters of men.

And here, as well as elsewhere, may be introduced a letter which bears
upon this question of self-control, written long years subsequent to the
period at which we have now arrived. I had been at Glasgow in 1855, at a
meeting of the British Association. On a certain day, I communicated a
paper to the physical section, which was followed by a brisk discussion.
Men of great distinction took part in it, the late Dr. Whewell among the
number, and it waxed warm on both sides. I was by no means content with
this discussion; and least of all, with my own part in it. This discontent
affected me for some days, during which I wrote to Faraday, giving him no
details, but expressing, in a general way, my dissatisfaction. I give the
following extract from his reply:—

'Sydenham, Oct. 6, 1855.

'My Dear Tyndall,—These great meetings, of which I think very well
altogether, advance science chiefly by bringing scientific men together
and making them to know and be friends with each other; and I am sorry
when that is not the effect in every part of their course. I know nothing
except from what you tell me, for I have not yet looked at the reports of
the proceedings; but let me, as an old man, who ought by this time to have
profited by experience, say that when I was younger I found I often
misinterpreted the intentions of people, and found they did not mean what
at the time I supposed they meant; and, further, that as a general rule,
it was better to be a little dull of apprehension where phrases seemed to
imply pique, and quick in perception when, on the contrary, they seemed to
imply kindly feeling. The real truth never fails ultimately to appear; and
opposing parties, if wrong, are sooner convinced when replied to
forbearingly, than when overwhelmed. All I mean to say is, that it is
better to be blind to the results of partisanship, and quick to see good
will. One has more happiness in oneself in endeavouring to follow the
things that make for peace. You can hardly imagine how often I have been
heated in private when opposed, as I have thought, unjustly and
superciliously, and yet I have striven, and succeeded, I hope, in keeping
down replies of the like kind. And I know I have never lost by it. I would
not say all this to you did I not esteem you as a true philosopher and
friend. (1)

'Yours, very truly,

'M. Faraday.'

Footnote to Chapter 4

(1) Faraday would have been rejoiced to learn that, during
its last meeting at Dundee, the British Association
illustrated in a striking manner the function which he here
describes as its principal one. In my own case, a brotherly
welcome was everywhere manifested. In fact, the differences
of really honourable and sane men are never beyond healing.

Chapter 5.

Identity of electricities; first researches on
electro-chemistry.

I have already once used the word 'discomfort' in reference to the
occasional state of Faraday's mind when experimenting. It was to him a
discomfort to reason upon data which admitted of doubt. He hated what he
called 'doubtful knowledge,' and ever tended either to transfer it into
the region of undoubtful knowledge, or of certain and definite ignorance.
Pretence of all kinds, whether in life or in philosophy, was hateful to
him. He wished to know the reality of our nescience as well as of our
science. 'Be one thing or the other,' he seemed to say to an unproved
hypothesis; 'come out as a solid truth, or disappear as a convicted lie.'
After making the great discovery which I have attempted to describe, a
doubt seemed to beset him as regards the identity of electricities. 'Is it
right,' he seemed to ask, 'to call this agency which I have discovered
electricity at all? Are there perfectly conclusive grounds for believing
that the electricity of the machine, the pile, the gymnotus and torpedo,
magneto-electricity and thermo-electricity, are merely different
manifestations of one and the same agent?' To answer this question to his
own satisfaction he formally reviewed the knowledge of that day. He added
to it new experiments of his own, and finally decided in favour of the
'Identity of Electricities.' His paper upon this subject was read before
the Royal Society on January 10 and 17, 1833.

After he had proved to his own satisfaction the identity of electricities,
he tried to compare them quantitatively together. The terms quantity and
intensity, which Faraday constantly used, need a word of explanation here.
He might charge a single Leyden jar by twenty turns of his machine, or he
might charge a battery of ten jars by the same number of turns. The
quantity in both cases would be sensibly the same, but the intensity of
the single jar would be the greatest, for here the electricity would be
less diffused. Faraday first satisfied himself that the needle of his
galvanometer was caused to swing through the same arc by the same quantity
of machine electricity, whether it was condensed in a small battery or
diffused over a large one. Thus the electricity developed by thirty turns
of his machine produced, under very variable conditions of battery
surface, the same deflection. Hence he inferred the possibility of
comparing, as regards quantity, electricities which differ greatly from
each other in intensity. His object now is to compare frictional with
voltaic electricity. Moistening bibulous paper with the iodide of
potassium—a favourite test of his—and subjecting it to the
action of machine electricity, he decomposed the iodide, and formed a
brown spot where the iodine was liberated. Then he immersed two wires, one
of zinc, the other of platinum, each 1/13th of an inch in diameter, to a
depth of 5/8ths of an inch in acidulated water during eight beats of his
watch, or 3/20ths of a second; and found that the needle of his
galvanometer swung through the same arc, and coloured his moistened paper
to the same extent, as thirty turns of his large electrical machine.
Twenty-eight turns of the machine produced an effect distinctly less than
that produced by his two wires. Now, the quantity of water decomposed by
the wires in this experiment totally eluded observation; it was
immeasurably small; and still that amount of decomposition involved the
development of a quantity of electric force which, if applied in a proper
form, would kill a rat, and no man would like to bear it.

In his subsequent researches 'On the absolute Quantity of Electricity
associated with the Particles or Atoms of matter,' he endeavours to give
an idea of the amount of electrical force involved in the decomposition of
a single grain of water. He is almost afraid to mention it, for he
estimates it at 800,000 discharges of his large Leyden battery. This, if
concentrated in a single discharge, would be equal to a very great flash
of lightning; while the chemical action of a single grain of water on four
grains of zinc would yield electricity equal in quantity to a powerful
thunderstorm. Thus his mind rises from the minute to the vast, expanding
involuntarily from the smallest laboratory fact till it embraces the
largest and grandest natural phenomena. (1)

In reality, however, he is at this time only clearing his way, and he
continues laboriously to clear it for some time afterwards. He is digging
the shaft, guided by that instinct towards the mineral lode which was to
him a rod of divination. 'Er riecht die Wahrheit,' said the lamented
Kohlrausch, an eminent German, once in my hearing:—'He smells the
truth.' His eyes are now steadily fixed on this wonderful voltaic current,
and he must learn more of its mode of transmission.

On May 23, 1833, he read a paper before the Royal Society 'On a new Law of
Electric Conduction.' He found that, though the current passed through
water, it did not pass through ice:—why not, since they are one and
the same substance? Some years subsequently he answered this question by
saying that the liquid condition enables the molecule of water to turn
round so as to place itself in the proper line of polarization, while the
rigidity of the solid condition prevents this arrangement. This polar
arrangement must precede decomposition, and decomposition is an
accompaniment of conduction. He then passed on to other substances; to
oxides and chlorides, and iodides, and salts, and sulphurets, and found
them all insulators when solid, and conductors when fused. In all cases,
moreover, except one—and this exception he thought might be apparent
only—he found the passage of the current across the fused compound
to be accompanied by its decomposition. Is then the act of decomposition
essential to the act of conduction in these bodies? Even recently this
question was warmly contested. Faraday was very cautious latterly in
expressing himself upon this subject; but as a matter of fact he held that
an infinitesimal quantity of electricity might pass through a compound
liquid without producing its decomposition. De la Rive, who has been a
great worker on the chemical phenomena of the pile, is very emphatic on
the other side. Experiment, according to him and others, establishes in
the most conclusive manner that no trace of electricity can pass through a
liquid compound without producing its equivalent decomposition. (2)

Faraday has now got fairly entangled amid the chemical phenomena of the
pile, and here his previous training under Davy must have been of the most
important service to him. Why, he asks, should decomposition thus take
place?—what force is it that wrenches the locked constituents of
these compounds asunder? On the 20th of June, 1833, he read a paper before
the Royal Society 'On Electro-chemical Decomposition,' in which he seeks
to answer these questions. The notion had been entertained that the poles,
as they are called, of the decomposing cell, or in other words the
surfaces by which the current enters and quits the liquid, exercised
electric attractions upon the constituents of the liquid and tore them
asunder. Faraday combats this notion with extreme vigour. Litmus reveals,
as you know, the action of an acid by turning red, turmeric reveals the
action of an alkali by turning brown. Sulphate of soda, you know, is a
salt compounded of the alkali soda and sulphuric acid. The voltaic current
passing through a solution of this salt so decomposes it, that sulphuric
acid appears at one pole of the decomposing cell and alkali at the other.
Faraday steeped a piece of litmus paper and a piece of turmeric paper in a
solution of sulphate of soda: placing each of them upon a separate plate
of glass, he connected them together by means of a string moistened with
the same solution. He then attached one of them to the positive conductor
of an electric machine, and the other to the gas-pipes of this building.
These he called his 'discharging train.' On turning the machine the
electricity passed from paper to paper through the string, which might be
varied in length from a few inches to seventy feet without changing the
result. The first paper was reddened, declaring the presence of sulphuric
acid; the second was browned, declaring the presence of the alkali soda.
The dissolved salt, therefore, arranged in this fashion, was decomposed by
the machine, exactly as it would have been by the voltaic current. When
instead of using the positive conductor he used the negative, the
positions of the acid and alkali were reversed. Thus he satisfied himself
that chemical decomposition by the machine is obedient to the laws which
rule decomposition by the pile.

And now he gradually abolishes those so-called poles, to the attraction of
which electric decomposition had been ascribed. He connected a piece of
turmeric paper moistened with the sulphate of soda with the positive
conductor of his machine; then he placed a metallic point in connection
with his discharging train opposite the moist paper, so that the
electricity should discharge through the air towards the point. The
turning of the machine caused the corners of the piece of turmeric paper
opposite to the point to turn brown, thus declaring the presence of
alkali. He changed the turmeric for litmus paper, and placed it, not in
connection with his conductor, but with his discharging train, a metallic
point connected with the conductor being fixed at a couple of inches from
the paper; on turning the machine, acid was liberated at the edges and
corners of the litmus. He then placed a series of pointed pieces of paper,
each separate piece being composed of two halves, one of litmus and the
other of turmeric paper, and all moistened with sulphate of soda, in the
line of the current from the machine. The pieces of paper were separated
from each other by spaces of air. The machine was turned; and it was
always found that at the point where the electricity entered the paper,
litmus was reddened, and at the point where it quitted the paper, turmeric
was browned. 'Here,' he urges, 'the poles are entirely abandoned, but we
have still electrochemical decomposition.' It is evident to him that
instead of being attracted by the poles, the bodies separated are ejected
by the current. The effects thus obtained with poles of air he also
succeeded in obtaining with poles of water. The advance in Faraday's own
ideas made at this time is indicated by the word 'ejected.' He afterwards
reiterates this view: the evolved substances are expelled from the
decomposing body, and 'not drawn out by an attraction.

Having abolished this idea of polar attraction, he proceeds to enunciate
and develop a theory of his own. He refers to Davy's celebrated Bakerian
Lecture, given in 1806, which he says 'is almost entirely occupied in the
consideration of electrochemical decompositions.' The facts recorded in
that lecture Faraday regards as of the utmost value. But 'the mode of
action by which the effects take place is stated very generally; so
generally, indeed, that probably a dozen precise schemes of
electrochemical action might be drawn up, differing essentially from each
other, yet all agreeing with the statement there given.'

It appears to me that these words might with justice be applied to
Faraday's own researches at this time. They furnish us with results of
permanent value; but little help can be found in the theory advanced to
account for them. It would, perhaps, be more correct to say that the
theory itself is hardly presentable in any tangible form to the intellect.
Faraday looks, and rightly looks, into the heart of the decomposing body
itself; he sees, and rightly sees, active within it the forces which
produce the decomposition, and he rejects, and rightly rejects, the notion
of external attraction; but beyond the hypothesis of decompositions and
recompositions, enunciated and developed by Grothuss and Davy, he does
not, I think, help us to any definite conception as to how the force
reaches the decomposing mass and acts within it. Nor, indeed, can this be
done, until we know the true physical process which underlies what we call
an electric current.

Faraday conceives of that current as 'an axis of power having contrary
forces exactly equal in amount in opposite directions'; but this
definition, though much quoted and circulated, teaches us nothing
regarding the current. An 'axis' here can only mean a direction; and what
we want to be able to conceive of is, not the axis along which the power
acts, but the nature and mode of action of the power itself. He objects to
the vagueness of De la Rive; but the fact is, that both he and De la Rive
labour under the same difficulty. Neither wishes to commit himself to the
notion of a current compounded of two electricities flowing in two
opposite directions: but the time had not come, nor is it yet come, for
the displacement of this provisional fiction by the true mechanical
conception. Still, however indistinct the theoretic notions of Faraday at
this time may be, the facts which are rising before him and around him are
leading him gradually, but surely, to results of incalculable importance
in relation to the philosophy of the voltaic pile.

He had always some great object of research in view, but in the pursuit of
it he frequently alighted on facts of collateral interest, to examine
which he sometimes turned aside from his direct course. Thus we find the
series of his researches on electrochemical decomposition interrupted by
an inquiry into 'the power of metals and other solids, to induce the
combination of gaseous bodies.' This inquiry, which was received by the
Royal Society on Nov. 30, 1833, though not so important as those which
precede and follow it, illustrates throughout his strength as an
experimenter. The power of spongy platinum to cause the combination of
oxygen and hydrogen had been discovered by Dobereiner in 1823, and had
been applied by him in the construction of his well-known philosophic
lamp. It was shown subsequently by Dulong and Thenard that even a platinum
wire, when perfectly cleansed, may be raised to incandescence by its
action on a jet of cold hydrogen.

In his experiments on the decomposition of water, Faraday found that the
positive platinum plate of the decomposing cell possessed in an
extraordinary degree the power of causing oxygen and hydrogen to combine.
He traced the cause of this to the perfect cleanness of the positive
plate. Against it was liberated oxygen, which, with the powerful affinity
of the 'nascent state,' swept away all impurity from the surface against
which it was liberated. The bubbles of gas liberated on one of the
platinum plates or wires of a decomposing cell are always much smaller,
and they rise in much more rapid succession than those from the other.
Knowing that oxygen is sixteen times heavier than hydrogen, I have more
than once concluded, and, I fear, led others into the error of concluding,
that the smaller and more quickly rising bubbles must belong to the
lighter gas. The thing appeared so obvious that I did not give myself the
trouble of looking at the battery, which would at once have told me the
nature of the gas. But Faraday would never have been satisfied with a
deduction if he could have reduced it to a fact. And he has taught me that
the fact here is the direct reverse of what I supposed it to be. The small
bubbles are oxygen, and their smallness is due to the perfect cleanness of
the surface on which they are liberated. The hydrogen adhering to the
other electrode swells into large bubbles, which rise in much slower
succession; but when the current is reversed, the hydrogen is liberated
upon the cleansed wire, and then its bubbles also become small.

Footnotes to Chapter 5

(1) Buff finds the quantity of electricity associated with
one milligramme of hydrogen in water to be equal to 45,480
charges of a Leyden jar, with a height of 480 millimetres,
and a diameter of 160 millimetres. Weber and Kohlrausch
have calculated that, if the quantity of electricity
associated with one milligramme of hydrogen in water were
diffused over a cloud at a height of 1000 metres above the
earth, it would exert upon an equal quantity of the opposite
electricity at the earth's surface an attractive force of
2,268,000 kilogrammes. (Electrolytische Maasbestimmungen,
1856, p. 262.)
(2) Faraday, sa Vie et ses Travaux, p. 20.

Chapter 6.

Laws of electro-chemical decomposition.

In our conceptions and reasonings regarding the forces of nature, we
perpetually make use of symbols which, when they possess a high
representative value, we dignify with the name of theories. Thus, prompted
by certain analogies, we ascribe electrical phenomena to the action of a
peculiar fluid, sometimes flowing, sometimes at rest. Such conceptions
have their advantages and their disadvantages; they afford peaceful
lodging to the intellect for a time, but they also circumscribe it, and
by-and-by, when the mind has grown too large for its lodging, it often
finds difficulty in breaking down the walls of what has become its prison
instead of its home. (1)

No man ever felt this tyranny of symbols more deeply than Faraday, and no
man was ever more assiduous than he to liberate himself from them, and the
terms which suggested them. Calling Dr. Whewell to his aid in 1833, he
endeavoured to displace by others all terms tainted by a foregone
conclusion. His paper on Electro-chemical Decomposition, received by the
Royal Society on January 9, 1834, opens with the proposal of a new
terminology. He would avoid the word 'current' if he could. (2) He does
abandon the word 'poles' as applied to the ends of a decomposing cell,
because it suggests the idea of attraction, substituting for it the
perfectly natural term Electrodes. He applied the term Electrolyte to
every substance which can be decomposed by the current, and the act of
decomposition he called Electrolysis. All these terms have become current
in science. He called the positive electrode the Anode, and the negative
one the Cathode, but these terms, though frequently used, have not enjoyed
the same currency as the others. The terms Anion and Cation, which he
applied to the constituents of the decomposed electrolyte, and the term
Ion, which included both anions and cations, are still less frequently
employed.

Faraday now passes from terminology to research; he sees the necessity of
quantitative determinations, and seeks to supply himself with a measure of
voltaic electricity. This he finds in the quantity of water decomposed by
the current. He tests this measure in all possible ways, to assure himself
that no error can arise from its employment. He places in the course of
one and the same current a series of cells with electrodes of different
sizes, some of them plates of platinum, others merely platinum wires, and
collects the gas liberated on each distinct pair of electrodes. He finds
the quantity of gas to be the same for all. Thus he concludes that when
the same quantity of electricity is caused to pass through a series of
cells containing acidulated water, the electro-chemical action is
independent of the size of the electrodes. (3) He next proves that
variations in intensity do not interfere with this equality of action.
Whether his battery is charged with strong acid or with weak; whether it
consists of five pairs or of fifty pairs; in short, whatever be its
source, when the same current is sent through his series of cells the same
amount of decomposition takes place in all. He next assures himself that
the strength or weakness of his dilute acid does not interfere with this
law. Sending the same current through a series of cells containing
mixtures of sulphuric acid and water of different strengths, he finds,
however the proportion of acid to water might vary, the same amount of gas
to be collected in all the cells. A crowd of facts of this character
forced upon Faraday's mind the conclusion that the amount of
electro-chemical decomposition depends, not upon the size of the
electrodes, not upon the intensity of the current, not upon the strength
of the solution, but solely upon the quantity of electricity which passes
through the cell. The quantity of electricity he concludes is proportional
to the amount of chemical action. On this law Faraday based the
construction of his celebrated Voltameter, or Measure of Voltaic
electricity.

But before he can apply this measure he must clear his ground of numerous
possible sources of error. The decomposition of his acidulated water is
certainly a direct result of the current; but as the varied and important
researches of MM. Becquerel, De la Rive, and others had shown, there are
also secondary actions which may materially interfere with and complicate
the pure action of the current. These actions may occur in two ways:
either the liberated ion may seize upon the electrode against which it is
set free, forming a chemical compound with that electrode; or it may seize
upon the substance of the electrolyte itself, and thus introduce into the
circuit chemical actions over and above those due to the current. Faraday
subjected these secondary actions to an exhaustive examination. Instructed
by his experiments, and rendered competent by them to distinguish between
primary and secondary results, he proceeds to establish the doctrine of
'Definite Electro-chemical Decomposition.'

Into the same circuit he introduced his voltameter, which consisted of a
graduated tube filled with acidulated water and provided with platinum
plates for the decomposition of the water, and also a cell containing
chloride of tin. Experiments already referred to had taught him that this
substance, though an insulator when solid, is a conductor when fused, the
passage of the current being always accompanied by the decomposition of
the chloride. He wished to ascertain what relation this decomposition bore
to that of the water in his voltameter.

Completing his circuit, he permitted the current to continue until 'a
reasonable quantity of gas' was collected in the voltameter. The circuit
was then broken, and the quantity of tin liberated compared with the
quantity of gas. The weight of the former was 3.2 grains, that of the
latter 0.49742 of a grain. Oxygen, as you know, unites with hydrogen in
the proportion of 8 to 1, to form water. Calling the equivalent, or as it
is sometimes called, the atomic weight of hydrogen 1, that of oxygen is 8;
that of water is consequently 8 + 1 or 9. Now if the quantity of water
decomposed in Faraday's experiment be represented by the number 9, or in
other words by the equivalent of water, then the quantity of tin liberated
from the fused chloride is found by an easy calculation to be 57.9, which
is almost exactly the chemical equivalent of tin. Thus both the water and
the chloride were broken up in proportions expressed by their respective
equivalents. The amount of electric force which wrenched asunder the
constituents of the molecule of water was competent, and neither more nor
less than competent, to wrench asunder the constituents of the molecules
of the chloride of tin. The fact is typical. With the indications of his
voltameter he compared the decompositions of other substances, both singly
and in series. He submitted his conclusions to numberless tests. He
purposely introduced secondary actions. He endeavoured to hamper the
fulfilment of those laws which it was the intense desire of his mind to
see established. But from all these difficulties emerged the golden truth,
that under every variety of circumstances the decompositions of the
voltaic current are as definite in their character as those chemical
combinations which gave birth to the atomic theory. This law of
Electro-chemical Decomposition ranks, in point of importance, with that of
Definite Combining Proportions in chemistry.

Footnotes to Chapter 6

(1) I copy these words from the printed abstract of a Friday
evening lecture, given by myself, because they remind me of
Faraday's voice, responding to the utterance by an emphatic
'hear! hear!'—Proceedings of the Royal Institution, vol.
ii. p. 132.
(2) In 1838 he expresses himself thus:—'The word current is
so expressive in common language that when applied in the
consideration of electrical phenomena, we can hardly divest
it sufficiently of its meaning, or prevent our minds from
being prejudiced by it.'—Exp. Resear., vol. i. p. 515. ($
1617.)
(3) This conclusion needs qualification. Faraday overlooked
the part played by ozone.

Chapter 7.

Origin of power in the voltaic pile.

In one of the public areas of the town of Como stands a statue with no
inscription on its pedestal, save that of a single name, 'Volta.' The
bearer of that name occupies a place for ever memorable in the history of
science. To him we owe the discovery of the voltaic pile, to which for a
brief interval we must now turn our attention.

The objects of scientific thought being the passionless laws and phenomena
of external nature, one might suppose that their investigation and
discussion would be completely withdrawn from the region of the feelings,
and pursued by the cold dry light of the intellect alone. This, however,
is not always the case. Man carries his heart with him into all his works.
You cannot separate the moral and emotional from the intellectual; and
thus it is that the discussion of a point of science may rise to the heat
of a battle-field. The fight between the rival optical theories of
Emission and Undulation was of this fierce character; and scarcely less
fierce for many years was the contest as to the origin and maintenance of
the power of the voltaic pile. Volta himself supposed it to reside in the
Contact of different metals. Here was exerted his 'Electro-motive force,'
which tore the combined electricities asunder and drove them as currents
in opposite directions. To render the circulation of the current possible,
it was necessary to connect the metals by a moist conductor; for when any
two metals were connected by a third, their relation to each other was
such that a complete neutralisation of the electric motion was the result.
Volta's theory of metallic contact was so clear, so beautiful, and
apparently so complete, that the best intellects of Europe accepted it as
the expression of natural law.

Volta himself knew nothing of the chemical phenomena of the pile; but as
soon as these became known, suggestions and intimations appeared that
chemical action, and not metallic contact, might be the real source of
voltaic electricity. This idea was expressed by Fabroni in Italy, and by
Wollaston in England. It was developed and maintained by those 'admirable
electricians,' Becquerel, of Paris, and De la Rive, of Geneva. The Contact
Theory, on the other hand, received its chief development and illustration
in Germany. It was long the scientific creed of the great chemists and
natural philosophers of that country, and to the present hour there may be
some of them unable to liberate themselves from the fascination of their
first-love.

After the researches which I have endeavoured to place before you, it was
impossible for Faraday to avoid taking a side in this controversy. He did
so in a paper 'On the Electricity of the Voltaic Pile,' received by the
Royal Society on the 7th of April, 1834. His position in the controversy
might have been predicted. He saw chemical effects going hand in hand with
electrical effects, the one being proportional to the other; and, in the
paper now before us, he proved that when the former was excluded, the
latter were sought for in vain. He produced a current without metallic
contact; he discovered liquids which, though competent to transmit the
feeblest currents—competent therefore to allow the electricity of
contact to flow through them if it were able to form a current—were
absolutely powerless when chemically inactive.

One of the very few experimental mistakes of Faraday occurred in this
investigation. He thought that with a single voltaic cell he had obtained
the spark before the metals touched, but he subsequently discovered his
error. To enable the voltaic spark to pass through air before the
terminals of the battery were united, it was necessary to exalt the
electro-motive force of the battery by multiplying its elements; but all
the elements Faraday possessed were unequal to the task of urging the
spark across the shortest measurable space of air. Nor, indeed, could the
action of the battery, the different metals of which were in contact with
each other, decide the point in question. Still, as regards the identity
of electricities from various sources, it was at that day of great
importance to determine whether or not the voltaic current could jump, as
a spark, across an interval before contact. Faraday's friend, Mr. Gassiot,
solved this problem. He erected a battery of 4000 cells, and with it urged
a stream of sparks from terminal to terminal, when separated from each
other by a measurable space of air.

The memoir on the 'Electricity of the Voltaic Pile,' published in 1834,
appears to have produced but little impression upon the supporters of the
contact theory. These indeed were men of too great intellectual weight and
insight lightly to take up, or lightly to abandon a theory. Faraday
therefore resumed the attack in a paper, communicated to the Royal Society
on the 6th of February, 1840. In this paper he hampered his antagonists by
a crowd of adverse experiments. He hung difficulty after difficulty about
the neck of the contact theory, until in its efforts to escape from his
assaults it so changed its character as to become a thing totally
different from the theory proposed by Volta. The more persistently it was
defended, however, the more clearly did it show itself to be a congeries
of devices, bearing the stamp of dialectic skill rather than of natural
truth.

In conclusion, Faraday brought to bear upon it an argument which, had its
full weight and purport been understood at the time, would have instantly
decided the controversy. 'The contact theory,' he urged, 'assumed that a
force which is able to overcome powerful resistance, as for instance that
of the conductors, good or bad, through which the current passes, and that
again of the electrolytic action where bodies are decomposed by it, can
arise out of nothing; that, without any change in the acting matter, or
the consumption of any generating force, a current shall be produced which
shall go on for ever against a constant resistance, or only be stopped, as
in the voltaic trough, by the ruins which its exertion has heaped up in
its own course. This would indeed be a creation of power, and is like no
other force in nature. We have many processes by which the form of the
power may be so changed, that an apparent conversion of one into the other
takes place. So we can change chemical force into the electric current, or
the current into chemical force. The beautiful experiments of Seebeck and
Peltier show the convertibility of heat and electricity; and others by
Oersted and myself show the convertibility of electricity and magnetism.
But in no case, not even in those of the Gymnotus and Torpedo, is there a
pure creation or a production of power without a corresponding exhaustion
of something to supply it.'

These words were published more than two years before either Mayer printed
his brief but celebrated essay on the Forces of Inorganic Nature, or Mr.
Joule published his first famous experiments on the Mechanical Value of
Heat. They illustrate the fact that before any great scientific principle
receives distinct enunciation by individuals, it dwells more or less
clearly in the general scientific mind. The intellectual plateau is
already high, and our discoverers are those who, like peaks above the
plateau, rise a little above the general level of thought at the time.

But many years prior even to the foregoing utterance of Faraday, a similar
argument had been employed. I quote here with equal pleasure and
admiration the following passage written by Dr. Roget so far back as 1829.
Speaking of the contact theory, he says:—'If there could exist a
power having the property ascribed to it by the hypothesis, namely, that
of giving continual impulse to a fluid in one constant direction, without
being exhausted by its own action, it would differ essentially from all
the known powers in nature. All the powers and sources of motion with the
operation of which we are acquainted, when producing these peculiar
effects, are expended in the same proportion as those effects are
produced; and hence arises the impossibility of obtaining by their agency
a perpetual effect; or in other words a perpetual motion. But the
electro-motive force, ascribed by Volta to the metals, when in contact, is
a force which, as long as a free course is allowed to the electricity it
sets in motion, is never expended, and continues to be excited with
undiminished power in the production of a never-ceasing effect. Against
the truth of such a supposition the probabilities are all but infinite.'
When this argument, which he employed independently, had clearly fixed
itself in his mind, Faraday never cared to experiment further on the
source of electricity in the voltaic pile. The argument appeared to him
'to remove the foundation itself of the contact theory,' and he afterwards
let it crumble down in peace. (1)

Footnote to Chapter 7

(1) To account for the electric current, which was really
the core of the whole discussion, Faraday demonstrated the
impotence of the Contact Theory as then enunciated and
defended. Still, it is certain that two different metals,
when brought into contact, charge themselves, the one with
positive and the other with negative electricity. I had the
pleasure of going over this ground with Kohlrausch in 1849,
and his experiments left no doubt upon my mind that the
contact electricity of Volta was a reality, though it could
produce no current. With one of the beautiful instruments
devised by himself, Sir William Thomson has rendered this
point capable of sure and easy demonstration; and he and
others now hold what may be called a contact theory, which,
while it takes into account the action of the metals, also
embraces the chemical phenomena of the circuit. Helmholtz,
I believe, was the first to give the contact theory this new
form, in his celebrated essay, Ueber die Erhaltung der
Kraft, p. 45.

Chapter 8.

The burst of power which had filled the four preceding years with an
amount of experimental work unparalleled in the history of science
partially subsided in 1835, and the only scientific paper contributed by
Faraday in that year was a comparatively unimportant one, 'On an improved
Form of the Voltaic Battery.' He brooded for a time: his experiments on
electrolysis had long filled his mind; he looked, as already stated, into
the very heart of the electrolyte, endeavouring to render the play of its
atoms visible to his mental eye. He had no doubt that in this case what is
called 'the electric current' was propagated from particle to particle of
the electrolyte; he accepted the doctrine of decomposition and
recomposition which, according to Grothuss and Davy, ran from electrode to
electrode. And the thought impressed him more and more that ordinary
electric induction was also transmitted and sustained by the action of
'contiguous particles.'

His first great paper on frictional electricity was sent to the Royal
Society on November 30, 1837. We here find him face to face with an idea
which beset his mind throughout his whole subsequent life,—the idea
of action at a distance. It perplexed and bewildered him. In his attempts
to get rid of this perplexity, he was often unconsciously rebelling
against the limitations of the intellect itself. He loved to quote Newton
upon this point; over and over again he introduces his memorable words,
'That gravity should be innate, inherent, and essential to matter, so that
one body may act upon another at a distance through a vacuum and without
the mediation of anything else, by and through which this action and force
may be conveyed from one to another, is to me so great an absurdity, that
I believe no man who has in philosophical matters a competent faculty of
thinking, can ever fall into it. Gravity must be caused by an agent acting
constantly according to certain laws; but whether this agent be material
or immaterial, I have left to the consideration of my readers.' (1)

Faraday does not see the same difficulty in his contiguous particles. And
yet, by transferring the conception from masses to particles, we simply
lessen size and distance, but we do not alter the quality of the
conception. Whatever difficulty the mind experiences in conceiving of
action at sensible distances, besets it also when it attempts to conceive
of action at insensible distances. Still the investigation of the point
whether electric and magnetic effects were wrought out through the
intervention of contiguous particles or not, had a physical interest
altogether apart from the metaphysical difficulty. Faraday grapples with
the subject experimentally. By simple intuition he sees that action at a
distance must be exerted in straight lines. Gravity, he knows, will not
turn a corner, but exerts its pull along a right line; hence his aim and
effort to ascertain whether electric action ever takes place in curved
lines. This once proved, it would follow that the action is carried on by
means of a medium surrounding the electrified bodies. His experiments in
1837 reduced, in his opinion, this point of demonstration. He then found
that he could electrify, by induction, an insulated sphere placed
completely in the shadow of a body which screened it from direct action.
He pictured the lines of electric force bending round the edges of the
screen, and reuniting on the other side of it; and he proved that in many
cases the augmentation of the distance between his insulated sphere and
the inducing body, instead of lessening, increased the charge of the
sphere. This he ascribed to the coalescence of the lines of electric force
at some distance behind the screen.

Faraday's theoretic views on this subject have not received general
acceptance, but they drove him to experiment, and experiment with him was
always prolific of results. By suitable arrangements he placed a metallic
sphere in the middle of a large hollow sphere, leaving a space of
something more than half an inch between them. The interior sphere was
insulated, the external one uninsulated. To the former he communicated a
definite charge of electricity. It acted by induction upon the concave
surface of the latter, and he examined how this act of induction was
effected by placing insulators of various kinds between the two spheres.
He tried gases, liquids, and solids, but the solids alone gave him
positive results. He constructed two instruments of the foregoing
description, equal in size and similar in form. The interior sphere of
each communicated with the external air by a brass stem ending in a knob.
The apparatus was virtually a Leyden jar, the two coatings of which were
the two spheres, with a thick and variable insulator between them. The
amount of charge in each jar was determined by bringing a proof-plane into
contact with its knob and measuring by a torsion balance the charge taken
away. He first charged one of his instruments, and then dividing the
charge with the other, found that when air intervened in both cases the
charge was equally divided. But when shellac, sulphur, or spermaceti was
interposed between the two spheres of one jar, while air occupied this
interval in the other, then he found that the instrument occupied by the
'solid dielectric' takes more than half the original charge. A portion of
the charge was absorbed by the dielectric itself. The electricity took
time to penetrate the dielectric. Immediately after the discharge of the
apparatus, no trace of electricity was found upon its knob. But after a
time electricity was found there, the charge having gradually returned
from the dielectric in which it had been lodged. Different insulators
possess this power of permitting the charge to enter them in different
degrees. Faraday figured their particles as polarized, and he concluded
that the force of induction is propagated from particle to particle of the
dielectric from the inner sphere to the outer one. This power of
propagation possessed by insulators he called their 'Specific Inductive
Capacity.'

Faraday visualizes with the utmost clearness the state of his contiguous
particles; one after another they become charged, each succeeding particle
depending for its charge upon its predecessor. And now he seeks to break
down the wall of partition between conductors and insulators. 'Can we
not,' he says, 'by a gradual chain of association carry up discharge from
its occurrence in air through spermaceti and water, to solutions, and then
on to chlorides, oxides, and metals, without any essential change in its
character?' Even copper, he urges, offers a resistance to the transmission
of electricity. The action of its particles differs from those of an
insulator only in degree. They are charged like the particles of the
insulator, but they discharge with greater ease and rapidity; and this
rapidity of molecular discharge is what we call conduction. Conduction
then is always preceded by atomic induction; and when, through some
quality of the body which Faraday does not define, the atomic discharge is
rendered slow and difficult, conduction passes into insulation.

Though they are often obscure, a fine vein of philosophic thought runs
through those investigations. The mind of the philosopher dwells amid
those agencies which underlie the visible phenomena of Induction and
Conduction; and he tries by the strong light of his imagination to see the
very molecules of his dielectrics. It would, however, be easy to criticise
these researches, easy to show the looseness, and sometimes the
inaccuracy, of the phraseology employed; but this critical spirit will get
little good out of Faraday. Rather let those who ponder his works seek to
realise the object he set before him, not permitting his occasional
vagueness to interfere with their appreciation of his speculations. We may
see the ripples, and eddies, and vortices of a flowing stream, without
being able to resolve all these motions into their constituent elements;
and so it sometimes strikes me that Faraday clearly saw the play of fluids
and ethers and atoms, though his previous training did not enable him to
resolve what he saw into its constituents, or describe it in a manner
satisfactory to a mind versed in mechanics. And then again occur, I
confess, dark sayings, difficult to be understood, which disturb my
confidence in this conclusion. It must, however, always be remembered that
he works at the very boundaries of our knowledge, and that his mind
habitually dwells in the 'boundless contiguity of shade' by which that
knowledge is surrounded.

In the researches now under review the ratio of speculation and reasoning
to experiment is far higher than in any of Faraday's previous works. Amid
much that is entangled and dark we have flashes of wondrous insight and
utterances which seem less the product of reasoning than of revelation. I
will confine myself here to one example of this divining power. By his
most ingenious device of a rapidly rotating mirror, Wheatstone had proved
that electricity required time to pass through a wire, the current
reaching the middle of the wire later than its two ends. 'If,' says
Faraday, 'the two ends of the wire in Professor Wheatstone's experiments
were immediately connected with two large insulated metallic surfaces
exposed to the air, so that the primary act of induction, after making the
contact for discharge, might be in part removed from the internal portion
of the wire at the first instance, and disposed for the moment on its
surface jointly with the air and surrounding conductors, then I venture to
anticipate that the middle spark would be more retarded than before. And
if those two plates were the inner and outer coatings of a large jar or
Leyden battery, then the retardation of the spark would be much greater.'
This was only a prediction, for the experiment was not made. (2) Sixteen
years subsequently, however, the proper conditions came into play, and
Faraday was able to show that the observations of Werner Siemens, and
Latimer Clark, on subterraneous and submarine wires were illustrations, on
a grand scale, of the principle which he had enunciated in 1838. The wires
and the surrounding water act as a Leyden jar, and the retardation of the
current predicted by Faraday manifests itself in every message sent by
such cables.

The meaning of Faraday in these memoirs on Induction and Conduction is, as
I have said, by no means always clear; and the difficulty will be most
felt by those who are best trained in ordinary theoretic conceptions. He
does not know the reader's needs, and he therefore does not meet them. For
instance he speaks over and over again of the impossibility of charging a
body with one electricity, though the impossibility is by no means
evident. The key to the difficulty is this. He looks upon every insulated
conductor as the inner coating of a Leyden jar. An insulated sphere in the
middle of a room is to his mind such a coating; the walls are the outer
coating, while the air between both is the insulator, across which the
charge acts by induction. Without this reaction of the walls upon the
sphere you could no more, according to Faraday, charge it with electricity
than you could charge a Leyden jar, if its outer coating were removed.
Distance with him is immaterial. His strength as a generalizer enables him
to dissolve the idea of magnitude; and if you abolish the walls of the
room—even the earth itself—he would make the sun and planets
the outer coating of his jar. I dare not contend that Faraday in these
memoirs made all his theoretic positions good. But a pure vein of
philosophy runs through these writings; while his experiments and
reasonings on the forms and phenomena of electrical discharge are of
imperishable importance.

Footnotes to Chapter 8

(1) Newton's third letter to Bentley.
(2) Had Sir Charles Wheatstone been induced to resume his
measurements, varying the substances through which, and the
conditions under which, the current is propagated, he might
have rendered great service to science, both theoretic and
experimental.

Chapter 9.

Rest needed—visit to Switzerland.

The last of these memoirs was dated from the Royal Institution in June,
1838. It concludes the first volume of his 'Experimental Researches on
Electricity.' In 1840, as already stated, he made his final assault on the
Contact Theory, from which it never recovered. (1) He was now feeling the
effects of the mental strain to which he had been subjected for so many
years. During these years he repeatedly broke down. His wife alone
witnessed the extent of his prostration, and to her loving care we, and
the world, are indebted for the enjoyment of his presence here so long. He
found occasional relief in a theatre. He frequently quitted London and
went to Brighton and elsewhere, always choosing a situation which
commanded a view of the sea, or of some other pleasant horizon, where he
could sit and gaze and feel the gradual revival of the faith that

'Nature never did betray
The heart that loved her.'

But very often for some days after his removal to the country, he would be
unable to do more than sit at a window and look out upon the sea and sky.

In 1841, his state became more serious than it had ever been before. A
published letter to Mr. Richard Taylor, dated March 11, 1843, contains an
allusion to his previous condition. 'You are aware,' he says, 'that
considerations regarding health have prevented me from working or reading
on science for the last two years.' This, at one period or another of
their lives, seems to be the fate of most great investigators. They do not
know the limits of their constitutional strength until they have
transgressed them. It is, perhaps, right that they should transgress them,
in order to ascertain where they lie. Faraday, however, though he went far
towards it, did not push his transgression beyond his power of
restitution. In 1841 Mrs. Faraday and he went to Switzerland, under the
affectionate charge of her brother, Mr. George Barnard, the artist. This
time of suffering throws fresh light upon his character. I have said that
sweetness and gentleness were not its only constituents; that he was also
fiery and strong. At the time now referred to, his fire was low and his
strength distilled away; but the residue of his life was neither
irritability nor discontent. He was unfit to mingle in society, for
conversation was a pain to him; but let us observe the great Man-child
when alone. He is at the village of Interlaken, enjoying Jungfrau sunsets,
and at times watching the Swiss nailers making their nails. He keeps a
little journal, in which he describes the process of nailmaking, and
incidentally throws a luminous beam upon himself.

'August 2, 1841.—Clout nailmaking goes on here rather considerably,
and is a very neat and pretty operation to observe. I love a smith's shop
and anything relating to smithery. My father was a smith.'

From Interlaken he went to the Falls of the Giessbach, on the pleasant
lake of Brientz. And here we have him watching the shoot of the cataract
down its series of precipices. It is shattered into foam at the base of
each, and tossed by its own recoil as water-dust through the air. The sun
is at his back, shining on the drifting spray, and he thus describes and
muses on what he sees:—

'August 12, 1841.—To-day every fall was foaming from the abundance
of water, and the current of wind brought down by it was in some places
too strong to stand against. The sun shone brightly, and the rainbows seen
from various points were very beautiful. One at the bottom of a fine but
furious fall was very pleasant,—there it remained motionless, whilst
the gusts and clouds of spray swept furiously across its place and were
dashed against the rock. It looked like a spirit strong in faith and
steadfast in the midst of the storm of passions sweeping across it, and
though it might fade and revive, still it held on to the rock as in hope
and giving hope. And the very drops, which in the whirlwind of their fury
seemed as if they would carry all away, were made to revive it and give it
greater beauty.'

Footnote to Chapter 9

(1) See note, p. 77.

Chapter 10.

Magnetization of light.

But we must quit the man and go on to the discoverer: we shall return for
a brief space to his company by-and-by. Carry your thoughts back to his
last experiments, and see him endeavouring to prove that induction is due
to the action of contiguous particles. He knew that polarized light was a
most subtle and delicate investigator of molecular condition. He used it
in 1834 in exploring his electrolytes, and he tried it in 1838 upon his
dielectrics. At that time he coated two opposite faces of a glass cube
with tinfoil, connected one coating with his powerful electric machine and
the other with the earth, and examined by polarized light the condition of
the glass when thus subjected to strong electric influence. He failed to
obtain any effect; still he was persuaded an action existed, and required
only suitable means to call it forth.

After his return from Switzerland he was beset by these thoughts; they
were more inspired than logical: but he resorted to magnets and proved his
inspiration true. His dislike of 'doubtful knowledge' and his efforts to
liberate his mind from the thraldom of hypotheses have been already
referred to. Still this rebel against theory was incessantly theorising
himself. His principal researches are all connected by an undercurrent of
speculation. Theoretic ideas were the very sap of his intellect—the
source from which all his strength as an experimenter was derived. While
once sauntering with him through the Crystal Palace, at Sydenham, I asked
him what directed his attention to the magnetization of light. It was his
theoretic notions. He had certain views regarding the unity and
convertibility of natural forces; certain ideas regarding the vibrations
of light and their relations to the lines of magnetic force; these views
and ideas drove him to investigation. And so it must always be: the great
experimentalist must ever be the habitual theorist, whether or not he
gives to his theories formal enunciation.

Faraday, you have been informed, endeavoured to improve the manufacture of
glass for optical purposes. But though he produced a heavy glass of great
refractive power, its value to optics did not repay him for the pains and
labour bestowed on it. Now, however, we reach a result established by
means of this same heavy glass, which made ample amends for all.

In November, 1845, he announced his discovery of the 'Magnetization of
Light and the Illumination of the Lines of Magnetic Force.' This title
provoked comment at the time, and caused misapprehension. He therefore
added an explanatory note; but the note left his meaning as entangled as
before. In fact Faraday had notions regarding the magnetization of light
which were peculiar to himself, and untranslatable into the scientific
language of the time. Probably no other philosopher of his day would have
employed the phrases just quoted as appropriate to the discovery announced
in 1845. But Faraday was more than a philosopher; he was a prophet, and
often wrought by an inspiration to be understood by sympathy alone. The
prophetic element in his character occasionally coloured, and even
injured, the utterance of the man of science; but subtracting that
element, though you might have conferred on him intellectual symmetry, you
would have destroyed his motive force.

But let us pass from the label of this casket to the jewel it contains. 'I
have long,' he says, 'held an opinion, almost amounting to conviction, in
common, I believe, with many other lovers of natural knowledge, that the
various forms under which the forces of matter are made manifest have one
common origin; in other words, are so directly related and mutually
dependent, that they are convertible, as it were, into one another, and
possess equivalents of power in their action.... This strong persuasion,'
he adds, 'extended to the powers of light.' And then he examines the
action of magnets upon light. From conversation with him and Anderson, I
should infer that the labour preceding this discovery was very great. The
world knows little of the toil of the discoverer. It sees the climber
jubilant on the mountain top, but does not know the labour expended in
reaching it. Probably hundreds of experiments had been made on transparent
crystals before he thought of testing his heavy glass. Here is his own
clear and simple description of the result of his first experiment with
this substance:—'A piece of this glass, about two inches square, and
0.5 of an inch thick, having flat and polished edges, was placed as a
diamagnetic (1) between the poles (not as yet magnetized by the electric
current), so that the polarized ray should pass through its length; the
glass acted as air, water, or any other transparent substance would do;
and if the eye-piece were previously turned into such a position that the
polarized ray was extinguished, or rather the image produced by it
rendered invisible, then the introduction of the glass made no alteration
in this respect. In this state of circumstances, the force of the
electro-magnet was developed by sending an electric current through its
coils, and immediately the image of the lamp-flame became visible and
continued so as long as the arrangement continued magnetic. On stopping
the electric current, and so causing the magnetic force to cease, the
light instantly disappeared. These phenomena could be renewed at pleasure,
at any instant of time, and upon any occasion, showing a perfect
dependence of cause and effect.'

In a beam of ordinary light the particles of the luminiferous ether
vibrate in all directions perpendicular to the line of progression; by the
act of polarization, performed here by Faraday, all oscillations but those
parallel to a certain plane are eliminated. When the plane of vibration of
the polarizer coincides with that of the analyzer, a portion of the beam
passes through both; but when these two planes are at right angles to each
other, the beam is extinguished. If by any means, while the polarizer and
analyzer remain thus crossed, the plane of vibration of the polarized beam
between them could be changed, then the light would be, in part at least,
transmitted. In Faraday's experiment this was accomplished. His magnet
turned the plane of polarization of the beam through a certain angle, and
thus enabled it to get through the analyzer; so that 'the magnetization of
light and the illumination of the magnetic lines of force' becomes, when
expressed in the language of modern theory, the rotation of the plane of
polarization.

To him, as to all true philosophers, the main value of a fact was its
position and suggestiveness in the general sequence of scientific truth.
Hence, having established the existence of a phenomenon, his habit was to
look at it from all possible points of view, and to develop its
relationship to other phenomena. He proved that the direction of the
rotation depends upon the polarity of his magnet; being reversed when the
magnetic poles are reversed. He showed that when a polarized ray passed
through his heavy glass in a direction parallel to the magnetic lines of
force, the rotation is a maximum, and that when the direction of the ray
is at right angles to the lines of force, there is no rotation at all. He
also proved that the amount of the rotation is proportional to the length
of the diamagnetic through which the ray passes. He operated with liquids
and solutions. Of aqueous solutions he tried 150 and more, and found the
power in all of them. He then examined gases; but here all his efforts to
produce any sensible action upon the polarized beam were ineffectual. He
then passed from magnets to currents, enclosing bars of heavy glass, and
tubes containing liquids and aqueous solutions within an electro-magnetic
helix. A current sent through the helix caused the plane of polarization
to rotate, and always in the direction of the current. The rotation was
reversed when the current was reversed. In the case of magnets, he
observed a gradual, though quick, ascent of the transmitted beam from a
state of darkness to its maximum brilliancy, when the magnet was excited.
In the case of currents, the beam attained at once its maximum. This he
showed to be due to the time required by the iron of the electro-magnet to
assume its full magnetic power, which time vanishes when a current,
without iron, is employed. 'In this experiment,' he says, 'we may, I
think, justly say that a ray of light is electrified, and the electric
forces illuminated.' In the helix, as with the magnets, he submitted air
to magnetic influence 'carefully and anxiously,' but could not discover
any trace of action on the polarized ray.

Many substances possess the power of turning the plane of polarization
without the intervention of magnetism. Oil of turpentine and quartz are
examples; but Faraday showed that, while in one direction, that is, across
the lines of magnetic force, his rotation is zero, augmenting gradually
from this until it attains its maximum, when the direction of the ray is
parallel to the lines of force; in the oil of turpentine the rotation is
independent of the direction of the ray. But he showed that a still more
profound distinction exists between the magnetic rotation and the natural
one. I will try to explain how. Suppose a tube with glass ends containing
oil of turpentine to be placed north and south. Fixing the eye at the
south end of the tube, let a polarized beam be sent through it from the
north. To the observer in this position the rotation of the plane of
polarization, by the turpentine, is right-handed. Let the eye be placed at
the north end of the tube, and a beam be sent through it from the south;
the rotation is still right-handed. Not so, however, when a bar of heavy
glass is subjected to the action of an electric current. In this case if,
in the first position of the eye, the rotation be right-handed, in the
second position it is left-handed. These considerations make it manifest
that if a polarized beam, after having passed through the oil of
turpentine in its natural state, could by any means be reflected back
through the liquid, the rotation impressed upon the direct beam would be
exactly neutralized by that impressed upon the reflected one. Not so with
the induced magnetic effect. Here it is manifest that the rotation would
be doubled by the act of reflection. Hence Faraday concludes that the
particles of the oil of turpentine which rotate by virtue of their natural
force, and those which rotate in virtue of the induced force, cannot be in
the same condition. The same remark applies to all bodies which possess a
natural power of rotating the plane of polarization.

And then he proceeded with exquisite skill and insight to take advantage
of this conclusion. He silvered the ends of his piece of heavy glass,
leaving, however, a narrow portion parallel to two edges diagonally
opposed to each other unsilvered. He then sent his beam through this
uncovered portion, and by suitably inclining his glass caused the beam
within it to reach his eye first direct, and then after two, four, and six
reflections. These corresponded to the passage of the ray once, three
times, five times, and seven times through the glass. He thus established
with numerical accuracy the exact proportionality of the rotation to the
distance traversed by the polarized beam. Thus in one series of
experiments where the rotation required by the direct beam was 12degrees,
that acquired by three passages through the glass was 36degrees, while
that acquired by five passages was 60degrees. But even when this method of
magnifying was applied, he failed with various solid substances to obtain
any effect; and in the case of air, though he employed to the utmost the
power which these repeated reflections placed in his hands, he failed to
produce the slightest sensible rotation.

These failures of Faraday to obtain the effect with gases seem to indicate
the true seat of the phenomenon. The luminiferous ether surrounds and is
influenced by the ultimate particles of matter. The symmetry of the one
involves that of the other. Thus, if the molecules of a crystal be
perfectly symmetrical round any line through the crystal, we may safely
conclude that a ray will pass along this line as through ordinary glass.
It will not be doubly refracted. From the symmetry of the liquid figures,
known to be produced in the planes of freezing, when radiant heat is sent
through ice, we may safely infer symmetry of aggregation, and hence
conclude that the line perpendicular to the planes of freezing is a line
of no double refraction; that it is, in fact, the optic axis of the
crystal. The same remark applies to the line joining the opposite blunt
angles of a crystal of Iceland spar. The arrangement of the molecules
round this line being symmetrical, the condition of the ether depending
upon these molecules shares their symmetry; and there is, therefore, no
reason why the wavelength should alter with the alteration of the azimuth
round this line. Annealed glass has its molecules symmetrically arranged
round every line that can be drawn through it; hence it is not doubly
refractive. But let the substance be either squeezed or strained in one
direction, the molecular symmetry, and with it the symmetry of the ether,
is immediately destroyed and the glass becomes doubly refractive. Unequal
heating produces the same effect. Thus mechanical strains reveal
themselves by optical effects; and there is little doubt that in Faraday's
experiment it is the magnetic strain that produces the rotation of the
plane of polarization. (2)

Footnotes to Chapter 10

(1) 'By a diamagnetic,' says Faraday, 'I mean a body through
which lines of magnetic force are passing, and which does
not by their action assume the usual magnetic state of iron
or loadstone.' Faraday subsequently used this term in a
different sense from that here given, as will immediately
appear.
(2) The power of double refraction conferred on the centre
of a glass rod, when it is caused to sound the fundamental
note due to its longitudinal vibration, and the absence of
the same power in the case of vibrating air (enclosed in a
glass organ-pipe), seems to be analogous to the presence and
absence of Faraday's effect in the same two substances.
Faraday never, to my knowledge, attempted to give, even in
conversation, a picture of the molecular condition of his
heavy glass when subjected to magnetic influence. In a
mathematical investigation of the subject, published in the
Proceedings of the Royal Society for 1856, Sir William
Thomson arrives at the conclusion that the 'diamagnetic' is
in a state of molecular rotation.

Chapter 11.

Discovery of diamagnetism—researches on magne-crystallic
action.

Faraday's next great step in discovery was announced in a memoir on the
'Magnetic Condition of all matter,' communicated to the Royal Society on
December 18, 1845. One great source of his success was the employment of
extraordinary power. As already stated, he never accepted a negative
answer to an experiment until he had brought to bear upon it all the force
at his command. He had over and over again tried steel magnets and
ordinary electro-magnets on various substances, but without detecting
anything different from the ordinary attraction exhibited by a few of
them. Stronger coercion, however, developed a new action. Before the pole
of an electro-magnet, he suspended a fragment of his famous heavy glass;
and observed that when the magnet was powerfully excited the glass fairly
retreated from the pole. It was a clear case of magnetic repulsion. He
then suspended a bar of the glass between two poles; the bar retreated
when the poles were excited, and set its length equatorially or at right
angles to the line joining them. When an ordinary magnetic body was
similarly suspended, it always set axially, that is, from pole to pole.

Faraday called those bodies which were repelled by the poles of a magnet,
diamagnetic bodies; using this term in a sense different from that in
which he employed it in his memoir on the magnetization of light. The term
magnetic he reserved for bodies which exhibited the ordinary attraction.
He afterwards employed the term magnetic to cover the whole phenomena of
attraction and repulsion, and used the word paramagnetic to designate such
magnetic action as is exhibited by iron.

Isolated observations by Brugmanns, Becquerel, Le Baillif, Saigy, and
Seebeck had indicated the existence of a repulsive force exercised by the
magnet on two or three substances; but these observations, which were
unknown to Faraday, had been permitted to remain without extension or
examination. Having laid hold of the fact of repulsion, Faraday
immediately expanded and multiplied it. He subjected bodies of the most
varied qualities to the action of his magnet:—mineral salts, acids,
alkalis, ethers, alcohols, aqueous solutions, glass, phosphorus, resins,
oils, essences, vegetable and animal tissues, and found them all amenable
to magnetic influence. No known solid or liquid proved insensible to the
magnetic power when developed in sufficient strength. All the tissues of
the human body, the blood—though it contains iron—included,
were proved to be diamagnetic. So that if you could suspend a man between
the poles of a magnet, his extremities would retreat from the poles until
his length became equatorial.

Soon after he had commenced his researches on diamagnetism, Faraday
noticed a remarkable phenomenon which first crossed my own path in the
following way: In the year 1849, while working in the cabinet of my
friend, Professor Knoblauch, of Marburg, I suspended a small copper coin
between the poles of an electro-magnet. On exciting the magnet, the coin
moved towards the poles and then suddenly stopped, as if it had struck
against a cushion. On breaking the circuit, the coin was repelled, the
revulsion being so violent as to cause it to spin several times round its
axis of suspension. A Silber-groschen similarly suspended exhibited the
same deportment. For a moment I thought this a new discovery; but on
looking over the literature of the subject, it appeared that Faraday had
observed, multiplied, and explained the same effect during his researches
on diamagnetism. His explanation was based upon his own great discovery of
magneto-electric currents. The effect is a most singular one. A weight of
several pounds of copper may be set spinning between the electro-magnetic
poles; the excitement of the magnet instantly stops the rotation. Though
nothing is apparent to the eye, the copper, if moved in the excited
magnetic field, appears to move through a viscous fluid; while, when a
flat piece of the metal is caused to pass to and fro like a saw between
the poles, the sawing of the magnetic field resembles the cutting through
of cheese or butter. (1) This virtual friction of the magnetic field is so
strong, that copper, by its rapid rotation between the poles, might
probably be fused. We may easily dismiss this experiment by saying that
the heat is due to the electric currents excited in the copper. But so
long as we are unable to reply to the question, 'What is an electric
current?' the explanation is only provisional. For my own part, I look
with profound interest and hope on the strange action here referred to.

Faraday's thoughts ran intuitively into experimental combinations, so that
subjects whose capacity for experimental treatment would, to ordinary
minds, seem to be exhausted in a moment, were shown by him to be all but
inexhaustible. He has now an object in view, the first step towards which
is the proof that the principle of Archimedes is true of magnetism. He
forms magnetic solutions of various degrees of strength, places them
between the poles of his magnet, and suspends in the solutions various
magnetic bodies. He proves that when the solution is stronger than the
body plunged in it, the body, though magnetic, is repelled; and when an
elongated piece of it is surrounded by the solution, it sets, like a
diamagnetic body, equatorially between the excited poles. The same body
when suspended in a solution of weaker magnetic power than itself, is
attracted as a whole, while an elongated portion of it sets axially.

And now theoretic questions rush in upon him. Is this new force a true
repulsion, or is it merely a differential attraction? Might not the
apparent repulsion of diamagnetic bodies be really due to the greater
attraction of the medium by which they are surrounded? He tries the
rarefaction of air, but finds the effect insensible. He is averse to
ascribing a capacity of attraction to space, or to any hypothetical medium
supposed to fill space. He therefore inclines, but still with caution, to
the opinion that the action of a magnet upon bismuth is a true and
absolute repulsion, and not merely the result of differential attraction.
And then he clearly states a theoretic view sufficient to account for the
phenomena. 'Theoretically,' he says, 'an explanation of the movements of
the diamagnetic bodies, and all the dynamic phenomena consequent upon the
action of magnets upon them, might be offered in the supposition that
magnetic induction caused in them a contrary state to that which it
produced in ordinary matter.' That is to say, while in ordinary magnetic
influence the exciting pole excites adjacent to itself the contrary
magnetism, in diamagnetic bodies the adjacent magnetism is the same as
that of the exciting pole. This theory of reversed polarity, however, does
not appear to have ever laid deep hold of Faraday's mind; and his own
experiments failed to give any evidence of its truth. He therefore
subsequently abandoned it, and maintained the non-polarity of the
diamagnetic force.

He then entered a new, though related field of inquiry. Having dealt with
the metals and their compounds, and having classified all of them that
came within the range of his observation under the two heads magnetic and
diamagnetic, he began the investigation of the phenomena presented by
crystals when subjected to magnetic power. This action of crystals had
been in part theoretically predicted by Poisson, (2) and actually
discovered by Plucker, whose beautiful results, at the period which we
have now reached, profoundly interested all scientific men. Faraday had
been frequently puzzled by the deportment of bismuth, a highly crystalline
metal. Sometimes elongated masses of the substance refused to set
equatorially, sometimes they set persistently oblique, and sometimes even,
like a magnetic body, from pole to pole.

'The effect,' he says, 'occurs at a single pole; and it is then striking
to observe a long piece of a substance so diamagnetic as bismuth repelled,
and yet at the same moment set round with force, axially, or end on, as a
piece of magnetic substance would do.' The effect perplexed him; and in
his efforts to release himself from this perplexity, no feature of this
new manifestation of force escaped his attention. His experiments are
described in a memoir communicated to the Royal Society on December 7,
1848.

I have worked long myself at magne-crystallic action, amid all the light
of Faraday's and Plucker's researches. The papers now before me were
objects of daily and nightly study with me eighteen or nineteen years ago;
but even now, though their perusal is but the last of a series of
repetitions, they astonish me. Every circumstance connected with the
subject; every shade of deportment; every variation in the energy of the
action; almost every application which could possibly be made of magnetism
to bring out in detail the character of this new force, is minutely
described. The field is swept clean, and hardly anything experimental is
left for the gleaner. The phenomena, he concludes, are altogether
different from those of magnetism or diamagnetism: they would appear, in
fact, to present to us 'a new force, or a new form of force, in the
molecules of matter,' which, for convenience sake, he designates by a new
word, as 'the magne-crystallic force.'

He looks at the crystal acted upon by the magnet. From its mass he passes,
in idea, to its atoms, and he asks himself whether the power which can
thus seize upon the crystalline molecules, after they have been fixed in
their proper positions by crystallizing force, may not, when they are
free, be able to determine their arrangement? He, therefore, liberates the
atoms by fusing the bismuth. He places the fused substance between the
poles of an electro-magnet, powerfully excited; but he fails to detect any
action. I think it cannot be doubted that an action is exerted here, that
a true cause comes into play; but its magnitude is not such as sensibly to
interfere with the force of crystallization, which, in comparison with the
diamagnetic force, is enormous. 'Perhaps,' adds Faraday, 'if a longer time
were allowed, and a permanent magnet used, a better result might be
obtained. I had built many hopes upon the process.' This expression, and
his writings abound in such, illustrates what has been already said
regarding his experiments being suggested and guided by his theoretic
conceptions. His mind was full of hopes and hypotheses, but he always
brought them to an experimental test. The record of his planned and
executed experiments would, I doubt not, show a high ratio of hopes
disappointed to hopes fulfilled; but every case of fulfilment abolished
all memory of defeat; disappointment was swallowed up in victory.

After the description of the general character of this new force, Faraday
states with the emphasis here reproduced its mode of action: 'The law of
action appears to be that the line or axis of MAGNE-CRYSTALLIC force
(being the resultant of the action of all the molecules) tends to place
itself parallel, or as a tangent, to the magnetic curve, or line of
magnetic force, passing through the place where the crystal is situated.'
The magne-crystallic force, moreover, appears to him 'to be clearly
distinguished from the magnetic or diamagnetic forces, in that it causes
neither approach nor recession, consisting not in attraction or repulsion,
but in giving a certain determinate position to the mass under its
influence.' And then he goes on 'very carefully to examine and prove the
conclusion that there was no connection of the force with attractive or
repulsive influences.' With the most refined ingenuity he shows that,
under certain circumstances, the magne-crystallic force can cause the
centre of gravity of a highly magnetic body to retreat from the poles, and
the centre of gravity of a highly diamagnetic body to approach them. His
experiments root his mind more and more firmly in the conclusion that
'neither attraction nor repulsion causes the set, or governs the final
position' of the crystal in the magnetic field. That the force which does
so is therefore 'distinct in its character and effects from the magnetic
and diamagnetic forms of force. On the other hand,' he continues, 'it has
a most manifest relation to the crystalline structure of bismuth and other
bodies, and therefore to the power by which their molecules are able to
build up the crystalline masses.'

And here follows one of those expressions which characterize the
conceptions of Faraday in regard to force generally:—'It appears to
me impossible to conceive of the results in any other way than by a mutual
reaction of the magnetic force, and the force of the particles of the
crystals upon each other.' He proves that the action of the force, though
thus molecular, is an action at a distance; he shows that a bismuth
crystal can cause a freely suspended magnetic needle to set parallel to
its magne-crystallic axis. Few living men are aware of the difficulty of
obtaining results like this, or of the delicacy necessary to their
attainment. 'But though it thus takes up the character of a force acting
at a distance, still it is due to that power of the particles which makes
them cohere in regular order and gives the mass its crystalline
aggregation, which we call at other times the attraction of aggregation,
and so often speak of as acting at insensible distances.' Thus he broods
over this new force, and looks at it from all possible points of
inspection. Experiment follows experiment, as thought follows thought. He
will not relinquish the subject as long as a hope exists of throwing more
light upon it. He knows full well the anomalous nature of the conclusion
to which his experiments lead him. But experiment to him is final, and he
will not shrink from the conclusion. 'This force,' he says, 'appears to me
to be very strange and striking in its character. It is not polar, for
there is no attraction or repulsion.' And then, as if startled by his own
utterance, he asks—'What is the nature of the mechanical force which
turns the crystal round, and makes it affect a magnet?'... 'I do not
remember,' he continues 'heretofore such a case of force as the present
one, where a body is brought into position only, without attraction or
repulsion.'

Plucker, the celebrated geometer already mentioned, who pursued
experimental physics for many years of his life with singular devotion and
success, visited Faraday in those days, and repeated before him his
beautiful experiments on magneto-optic action. Faraday repeated and
verified Plucker's observations, and concluded, what he at first seemed to
doubt, that Plucker's results and magne-crystallic action had the same
origin.

At the end of his papers, when he takes a last look along the line of
research, and then turns his eyes to the future, utterances quite as much
emotional as scientific escape from Faraday. 'I cannot,' he says, at the
end of his first paper on magne-crystallic action, 'conclude this series
of researches without remarking how rapidly the knowledge of molecular
forces grows upon us, and how strikingly every investigation tends to
develop more and more their importance, and their extreme attraction as an
object of study. A few years ago magnetism was to us an occult power,
affecting only a few bodies, now it is found to influence all bodies, and
to possess the most intimate relations with electricity, heat, chemical
action, light, crystallization, and through it, with the forces concerned
in cohesion; and we may, in the present state of things, well feel urged
to continue in our labours, encouraged by the hope of bringing it into a
bond of union with gravity itself.'

Supplementary remarks

A brief space will, perhaps, be granted me here to state the further
progress of an investigation which interested Faraday so much. Drawn by
the fame of Bunsen as a teacher, in the year 1848 I became a student in
the University of Marburg, in Hesse Cassel. Bunsen's behaviour to me was
that of a brother as well as that of a teacher, and it was also my
happiness to make the acquaintance and gain the friendship of Professor
Knoblauch, so highly distinguished by his researches on Radiant Heat.
Plucker's and Faraday's investigations filled all minds at the time, and
towards the end of 1849, Professor Knoblauch and myself commenced a joint
investigation of the entire question. Long discipline was necessary to
give us due mastery over it. Employing a method proposed by Dove, we
examined the optical properties of our crystals ourselves; and these
optical observations went hand in hand with our magnetic experiments. The
number of these experiments was very great, but for a considerable time no
fact of importance was added to those already published. At length,
however, it was our fortune to meet with various crystals whose deportment
could not be brought under the laws of magne-crystallic action enunciated
by Plucker. We also discovered instances which led us to suppose that the
magne-crystallic force was by no means independent, as alleged, of the
magnetism or diamagnetism of the mass of the crystal. Indeed, the more we
worked at the subject, the more clearly did it appear to us that the
deportment of crystals in the magnetic field was due, not to a force
previously unknown, but to the modification of the known forces of
magnetism and diamagnetism by crystalline aggregation.

An eminent example of magne-crystallic action adduced by Plucker, and
experimented on by Faraday, was Iceland spar. It is what in optics is
called a negative crystal, and according to the law of Plucker, the axis
of such a crystal was always repelled by a magnet. But we showed that it
was only necessary to substitute, in whole or in part, carbonate of iron
for carbonate of lime, thus changing the magnetic but not the optical
character of the crystal, to cause the axis to be attracted. That the
deportment of magnetic crystals is exactly antithetical to that of
diamagnetic crystals isomorphous with the magnetic ones, was proved to be
a general law of action. In all cases, the line which in a diamagnetic
crystal set equatorially, always set itself in an isomorphous magnetic
crystal axially. By mechanical compression other bodies were also made to
imitate the Iceland spar.

These and numerous other results bearing upon the question were published
at the time in the 'Philosophical Magazine' and in 'Poggendorff's
Annalen'; and the investigation of diamagnetism and magne-crystallic
action was subsequently continued by me in the laboratory of Professor
Magnus of Berlin. In December, 1851, after I had quitted Germany, Dr.
Bence Jones went to the Prussian capital to see the celebrated experiments
of Du Bois Reymond. Influenced, I suppose, by what he there heard, he
afterwards invited me to give a Friday evening discourse at the Royal
Institution. I consented, not without fear and trembling. For the Royal
Institution was to me a kind of dragon's den, where tact and strength
would be necessary to save me from destruction. On February 11, 1853, the
discourse was given, and it ended happily. I allude to these things, that
I may mention that, though my aim and object in that lecture was to
subvert the notions both of Faraday and Plucker, and to establish in
opposition to their views what I regarded as the truth, it was very far
from producing in Faraday either enmity or anger. At the conclusion of the
lecture, he quitted his accustomed seat, crossed the theatre to the corner
into which I had shrunk, shook me by the hand, and brought me back to the
table. Once more, subsequently, and in connection with a related question,
I ventured to differ from him still more emphatically. It was done out of
trust in the greatness of his character; nor was the trust misplaced. He
felt my public dissent from him; and it pained me afterwards to the quick
to think that I had given him even momentary annoyance. It was, however,
only momentary. His soul was above all littleness and proof to all
egotism. He was the same to me afterwards that he had been before; the
very chance expression which led me to conclude that he felt my dissent
being one of kindness and affection.

It required long subsequent effort to subdue the complications of
magne-crystallic action, and to bring under the dominion of elementary
principles the vast mass of facts which the experiments of Faraday and
Plucker had brought to light. It was proved by Reich, Edmond Becquerel,
and myself, that the condition of diamagnetic bodies, in virtue of which
they were repelled by the poles of a magnet, was excited in them by those
poles; that the strength of this condition rose and fell with, and was
proportional to, the strength of the acting magnet. It was not then any
property possessed permanently by the bismuth, and which merely required
the development of magnetism to act upon it, that caused the repulsion;
for then the repulsion would have been simply proportional to the strength
of the influencing magnet, whereas experiment proved it to augment as the
square of the strength. The capacity to be repelled was therefore not
inherent in the bismuth, but induced. So far an identity of action was
established between magnetic and diamagnetic bodies. After this the
deportment of magnetic bodies, 'normal' and 'abnormal'; crystalline,
amorphous, and compressed, was compared with that of crystalline,
amorphous, and compressed diamagnetic bodies; and by a series of
experiments, executed in the laboratory of this Institution, the most
complete antithesis was established between magnetism and diamagnetism.
This antithesis embraced the quality of polarity,—the theory of
reversed polarity, first propounded by Faraday, being proved to be true.
The discussion of the question was very brisk. On the Continent Professor
Wilhelm Weber was the ablest and most successful supporter of the doctrine
of diamagnetic polarity; and it was with an apparatus, devised by him and
constructed under his own superintendence, by Leyser of Leipzig, that the
last demands of the opponents of diamagnetic polarity were satisfied. The
establishment of this point was absolutely necessary to the explanation of
magne-crystallic action.

With that admirable instinct which always guided him, Faraday had seen
that it was possible, if not probable, that the diamagnetic force acts
with different degrees of intensity in different directions, through the
mass of a crystal. In his studies on electricity, he had sought an
experimental reply to the question whether crystalline bodies had not
different specific inductive capacities in different directions, but he
failed to establish any difference of the kind. His first attempt to
establish differences of diamagnetic action in different directions
through bismuth, was also a failure; but he must have felt this to be a
point of cardinal importance, for he returned to the subject in 1850, and
proved that bismuth was repelled with different degrees of force in
different directions. It seemed as if the crystal were compounded of two
diamagnetic bodies of different strengths, the substance being more
strongly repelled across the magne-crystallic axis than along it. The same
result was obtained independently, and extended to various other bodies,
magnetic as well as diamagnetic, and also to compressed substances, a
little subsequently by myself.

The law of action in relation to this point is, that in diamagnetic
crystals, the line along which the repulsion is a maximum, sets
equatorially in the magnetic field; while in magnetic crystals the line
along which the attraction is a maximum sets from pole to pole. Faraday
had said that the magne-crystallic force was neither attraction nor
repulsion. Thus far he was right. It was neither taken singly, but it was
both. By the combination of the doctrine of diamagnetic polarity with
these differential attractions and repulsions, and by paying due regard to
the character of the magnetic field, every fact brought to light in the
domain of magne-crystallic action received complete explanation. The most
perplexing of those facts were shown to result from the action of
mechanical couples, which the proved polarity both of magnetism and
diamagnetism brought into play. Indeed the thoroughness with which the
experiments of Faraday were thus explained, is the most striking possible
demonstration of the marvellous precision with which they were executed.

Footnotes to Chapter 11

Chapter 12.

Magnetism of flame and gases—atmospheric magnetism

When an experimental result was obtained by Faraday it was instantly
enlarged by his imagination. I am acquainted with no mind whose power and
suddenness of expansion at the touch of new physical truth could be ranked
with his. Sometimes I have compared the action of his experiments on his
mind to that of highly combustible matter thrown into a furnace; every
fresh entry of fact was accompanied by the immediate development of light
and heat. The light, which was intellectual, enabled him to see far beyond
the boundaries of the fact itself, and the heat, which was emotional,
urged him to the conquest of this newly-revealed domain. But though the
force of his imagination was enormous, he bridled it like a mighty rider,
and never permitted his intellect to be overthrown.

In virtue of the expansive power which his vivid imagination conferred
upon him, he rose from the smallest beginnings to the grandest ends.
Having heard from Zantedeschi that Bancalari had established the magnetism
of flame, he repeated the experiments and augmented the results. He passed
from flames to gases, examining and revealing their magnetic and
diamagnetic powers; and then he suddenly rose from his bubbles of oxygen
and nitrogen to the atmospheric envelope of the earth itself, and its
relations to the great question of terrestrial magnetism. The rapidity
with which these ever-augmenting thoughts assumed the form of experiments
is unparalleled. His power in this respect is often best illustrated by
his minor investigations, and, perhaps, by none more strikingly than by
his paper 'On the Diamagnetic Condition of Flame and Gases,' published as
a letter to Mr. Richard Taylor, in the 'Philosophical Magazine' for
December, 1847. After verifying, varying, and expanding the results of
Bancalari, he submitted to examination heated air-currents, produced by
platinum spirals placed in the magnetic field, and raised to incandescence
by electricity. He then examined the magnetic deportment of gases
generally. Almost all of these gases are invisible; but he must,
nevertheless, track them in their unseen courses. He could not effect this
by mingling smoke with his gases, for the action of his magnet upon the
smoke would have troubled his conclusions. He, therefore, 'caught' his
gases in tubes, carried them out of the magnetic field, and made them
reveal themselves at a distance from the magnet.

Immersing one gas in another, he determined their differential action;
results of the utmost beauty being thus arrived at. Perhaps the most
important are those obtained with atmospheric air and its two
constituents. Oxygen, in various media, was strongly attracted by the
magnet; in coal-gas, for example, it was powerfully magnetic, whereas
nitrogen was diamagnetic. Some of the effects obtained with oxygen in
coal-gas were strikingly beautiful. When the fumes of chloride of ammonium
(a diamagnetic substance) were mingled with the oxygen, the cloud of
chloride behaved in a most singular manner,—'The attraction of iron
filings,' says Faraday, 'to a magnetic pole is not more striking than the
appearance presented by the oxygen under these circumstances.'

On observing this deportment the question immediately occurs to him,—Can
we not separate the oxygen of the atmosphere from its nitrogen by magnetic
analysis? It is the perpetual occurrence of such questions that marks the
great experimenter. The attempt to analyze atmospheric air by magnetic
force proved a failure, like the previous attempt to influence
crystallization by the magnet. The enormous comparative power of the force
of crystallization I have already assigned as a reason for the
incompetence of the magnet to determine molecular arrangement; in the
present instance the magnetic analysis is opposed by the force of
diffusion, which is also very strong comparatively. The same remark
applies to, and is illustrated by, another experiment subsequently
executed by Faraday. Water is diamagnetic, sulphate of iron is strongly
magnetic. He enclosed 'a dilute solution of sulphate of iron in a tube,
and placed the lower end of the tube between the poles of a powerful
horseshoe magnet for days together,' but he could produce 'no
concentration of the solution in the part near the magnet.' Here also the
diffusibility of the salt was too powerful for the force brought against
it.

The experiment last referred to is recorded in a paper presented to the
Royal Society on the 2nd August, 1850, in which he pursues the
investigation of the magnetism of gases. Newton's observations on
soap-bubbles were often referred to by Faraday. His delight in a
soap-bubble was like that of a boy, and he often introduced them into his
lectures, causing them, when filled with air, to float on invisible seas
of carbonic acid, and otherwise employing them as a means of illustration.
He now finds them exceedingly useful in his experiments on the magnetic
condition of gases. A bubble of air in a magnetic field occupied by air
was unaffected, save through the feeble repulsion of its envelope. A
bubble of nitrogen, on the contrary, was repelled from the magnetic axis
with a force far surpassing that of a bubble of air. The deportment of
oxygen in air 'was very impressive, the bubble being pulled inward or
towards the axial line, sharply and suddenly, as if the oxygen were highly
magnetic.'

He next labours to establish the true magnetic zero, a problem not so easy
as might at first sight be imagined. For the action of the magnet upon any
gas, while surrounded by air or any other gas, can only be differential;
and if the experiment were made in vacuo, the action of the envelope, in
this case necessarily of a certain thickness, would trouble the result.
While dealing with this subject, Faraday makes some noteworthy
observations regarding space. In reference to the Torricellian vacuum, he
says, 'Perhaps it is hardly necessary for me to state that I find both
iron and bismuth in such vacua perfectly obedient to the magnet. From such
experiments, and also from general observations and knowledge, it seems
manifest that the lines of magnetic force can traverse pure space, just as
gravitating force does, and as statical electrical forces do, and
therefore space has a magnetic relation of its own, and one that we shall
probably find hereafter to be of the utmost importance in natural
phenomena. But this character of space is not of the same kind as that
which, in relation to matter, we endeavour to express by the terms
magnetic and diamagnetic. To confuse these together would be to confound
space with matter, and to trouble all the conceptions by which we
endeavour to understand and work out a progressively clearer view of the
mode of action, and the laws of natural forces. It would be as if in
gravitation or electric forces, one were to confound the particles acting
on each other with the space across which they are acting, and would, I
think, shut the door to advancement. Mere space cannot act as matter acts,
even though the utmost latitude be allowed to the hypothesis of an ether;
and admitting that hypothesis, it would be a large additional assumption
to suppose that the lines of magnetic force are vibrations carried on by
it, whilst as yet we have no proof that time is required for their
propagation, or in what respect they may, in general character, assimilate
to or differ from their respective lines of gravitating, luminiferous, or
electric forces.'

Pure space he assumes to be the true magnetic zero, but he pushes his
inquiries to ascertain whether among material substances there may not be
some which resemble space. If you follow his experiments, you will soon
emerge into the light of his results. A torsion-beam was suspended by a
skein of cocoon silk; at one end of the beam was fixed a cross-piece 1 1/2
inch long. Tubes of exceedingly thin glass, filled with various gases, and
hermetically sealed, were suspended in pairs from the two ends of the
cross-piece. The position of the rotating torsion-head was such that the
two tubes were at opposite sides of, and equidistant from, the magnetic
axis, that is to say from the line joining the two closely approximated
polar points of an electro-magnet. His object was to compare the magnetic
action of the gases in the two tubes. When one tube was filled with
oxygen, and the other with nitrogen, on the supervention of the magnetic
force, the oxygen was pulled towards the axis, the nitrogen being pushed
out. By turning the torsion-head they could be restored to their primitive
position of equidistance, where it is evident the action of the glass
envelopes was annulled. The amount of torsion necessary to re-establish
equidistance expressed the magnetic difference of the substances compared.

And then he compared oxygen with oxygen at different pressures. One of his
tubes contained the gas at the pressure of 30 inches of mercury, another
at a pressure of 15 inches of mercury, a third at a pressure of 10 inches,
while a fourth was exhausted as far as a good air-pump renders exhaustion
possible. 'When the first of these was compared with the other three, the
effect was most striking.' It was drawn towards the axis when the magnet
was excited, the tube containing the rarer gas being apparently driven
away, and the greater the difference between the densities of the two
gases, the greater was the energy of this action.

And now observe his mode of reaching a material magnetic zero. When a
bubble of nitrogen was exposed in air in the magnetic field, on the
supervention of the power, the bubble retreated from the magnet. A less
acute observer would have set nitrogen down as diamagnetic; but Faraday
knew that retreat, in a medium composed in part of oxygen, might be due to
the attraction of the latter gas, instead of to the repulsion of the gas
immersed in it. But if nitrogen be really diamagnetic, then a bubble or
bulb filled with the dense gas will overcome one filled with the rarer
gas. From the cross-piece of his torsion-balance he suspended his bulbs of
nitrogen, at equal distances from the magnetic axis, and found that the
rarefaction, or the condensation of the gas in either of the bulbs had not
the slightest influence. When the magnetic force was developed, the bulbs
remained in their first position, even when one was filled with nitrogen,
and the other as far as possible exhausted. Nitrogen, in fact, acted 'like
space itself'; it was neither magnetic nor diamagnetic.

He cannot conveniently compare the paramagnetic force of oxygen with iron,
in consequence of the exceeding magnetic intensity of the latter
substance; but he does compare it with the sulphate of iron, and finds
that, bulk for bulk, oxygen is equally magnetic with a solution of this
substance in water 'containing seventeen times the weight of the oxygen in
crystallized proto-sulphate of iron, or 3.4 times its weight of metallic
iron in that state of combination.' By its capability to deflect a fine
glass fibre, he finds that the attraction of this bulb of oxygen,
containing only 0.117 of a grain of the gas, at an average distance of
more than an inch from the magnetic axis, is about equal to the
gravitating force of the same amount of oxygen as expressed by its weight.

These facts could not rest for an instant in the mind of Faraday without
receiving that expansion to which I have already referred. 'It is hardly
necessary,' he writes, 'for me to say here that this oxygen cannot exist
in the atmosphere exerting such a remarkable and high amount of magnetic
force, without having a most important influence on the disposition of the
magnetism of the earth, as a planet; especially if it be remembered that
its magnetic condition is greatly altered by variations of its density and
by variations of its temperature. I think I see here the real cause of
many of the variations of that force, which have been, and are now so
carefully watched on different parts of the surface of the globe. The
daily variation, and the annual variation, both seem likely to come under
it; also very many of the irregular continual variations, which the
photographic process of record renders so beautifully manifest. If such
expectations be confirmed, and the influence of the atmosphere be found
able to produce results like these, then we shall probably find a new
relation between the aurora borealis and the magnetism of the earth,
namely, a relation established, more or less, through the air itself in
connection with the space above it; and even magnetic relations and
variations, which are not as yet suspected, may be suggested and rendered
manifest and measurable, in the further development of what I will venture
to call Atmospheric Magnetism. I may be over-sanguine in these
expectations, but as yet I am sustained in them by the apparent reality,
simplicity, and sufficiency of the cause assumed, as it at present appears
to my mind. As soon as I have submitted these views to a close
consideration, and the test of accordance with observation, and, where
applicable, with experiments also, I will do myself the honour to bring
them before the Royal Society.'

Two elaborate memoirs are then devoted to the subject of Atmospheric
Magnetism; the first sent to the Royal Society on the 9th of October, and
the second on the 19th of November, 1850. In these memoirs he discusses
the effects of heat and cold upon the magnetism of the air, and the action
on the magnetic needle, which must result from thermal changes. By the
convergence and divergence of the lines of terrestrial magnetic force, he
shows how the distribution of magnetism, in the earth's atmosphere, is
effected. He applies his results to the explanation of the Annual and of
the Diurnal Variation: he also considers irregular variations, including
the action of magnetic storms. He discusses, at length, the observations
at St. Petersburg, Greenwich, Hobarton, St. Helena, Toronto, and the Cape
of Good Hope; believing that the facts, revealed by his experiments,
furnish the key to the variations observed at all these places.

In the year 1851, I had the honour of an interview with Humboldt, in
Berlin, and his parting words to me then were, 'Tell Faraday that I
entirely agree with him, and that he has, in my opinion, completely
explained the variation of the declination.' Eminent men have since
informed me that Humboldt was hasty in expressing this opinion. In fact,
Faraday's memoirs on atmospheric magnetism lost much of their force—perhaps
too much—through the important discovery of the relation of the
variation of the declination to the number of the solar spots. But I agree
with him and M. Edmond Becquerel, who worked independently at this
subject, in thinking, that a body so magnetic as oxygen, swathing the
earth, and subject to variations of temperature, diurnal and annual, must
affect the manifestations of terrestrial magnetism. (1) The air that
stands upon a single square foot of the earth's surface is, according to
Faraday, equivalent in magnetic force to 8160 lbs. of crystallized
protosulphate of iron. Such a substance cannot be absolutely neutral as
regards the deportment of the magnetic needle. But Faraday's writings on
this subject are so voluminous, and the theoretic points are so novel and
intricate, that I shall postpone the complete analysis of these researches
to a time when I can lay hold of them more completely than my other duties
allow me to do now.

Footnote to Chapter 12

(1) This persuasion has been greatly strengthened by the
recent perusal of a paper by Mr. Baxendell.

Chapter 13.

Speculations: nature of matter: lines of force

The scientific picture of Faraday would not be complete without a
reference to his speculative writings. On Friday, January 19, 1844, he
opened the weekly evening-meetings of the Royal Institution by a discourse
entitled 'A speculation touching Electric Conduction and the nature of
Matter.' In this discourse he not only attempts the overthrow of Dalton's
Theory of Atoms, but also the subversion of all ordinary scientific ideas
regarding the nature and relations of Matter and Force. He objected to the
use of the term atom:—'I have not yet found a mind,' he says, 'that
did habitually separate it from its accompanying temptations; and there
can be no doubt that the words definite proportions, equivalent, primes,
&c., which did and do fully express all the facts of what is usually
called the atomic theory in chemistry, were dismissed because they were
not expressive enough, and did not say all that was in the mind of him who
used the word atom in their stead.'

A moment will be granted me to indicate my own view of Faraday's position
here. The word 'atom' was not used in the stead of definite proportions,
equivalents, or primes. These terms represented facts that followed from,
but were not equivalent to, the atomic theory. Facts cannot satisfy the
mind: and the law of definite combining proportions being once
established, the question 'why should combination take place according to
that law?' is inevitable. Dalton answered this question by the enunciation
of the Atomic Theory, the fundamental idea of which is, in my opinion,
perfectly secure. The objection of Faraday to Dalton might be urged with
the same substantial force against Newton: it might be stated with regard
to the planetary motions that the laws of Kepler revealed the facts; that
the introduction of the principle of gravitation was an addition to the
facts. But this is the essence of all theory. The theory is the backward
guess from fact to principle; the conjecture, or divination regarding
something, which lies behind the facts, and from which they flow in
necessary sequence. If Dalton's theory, then, account for the definite
proportions observed in the combinations of chemistry, its justification
rests upon the same basis as that of the principle of gravitation. All
that can in strictness be said in either case is that the facts occur as
if the principle existed.

The manner in which Faraday himself habitually deals with his hypotheses
is revealed in this lecture. He incessantly employed them to gain
experimental ends, but he incessantly took them down, as an architect
removes the scaffolding when the edifice is complete. 'I cannot but
doubt,' he says, 'that he who as a mere philosopher has most power of
penetrating the secrets of nature, and guessing by hypothesis at her mode
of working, will also be most careful for his own safe progress and that
of others, to distinguish the knowledge which consists of assumption, by
which I mean theory and hypothesis, from that which is the knowledge of
facts and laws.' Faraday himself, in fact, was always 'guessing by
hypothesis,' and making theoretic divination the stepping-stone to his
experimental results.

I have already more than once dwelt on the vividness with which he
realised molecular conditions; we have a fine example of this strength and
brightness of imagination in the present 'speculation.' He grapples with
the notion that matter is made up of particles, not in absolute contact,
but surrounded by interatomic space. 'Space,' he observes, 'must be taken
as the only continuous part of a body so constituted. Space will permeate
all masses of matter in every direction like a net, except that in place
of meshes it will form cells, isolating each atom from its neighbours,
itself only being continuous.'

Let us follow out this notion; consider, he argues, the case of a
non-conductor of electricity, such for example as shell-lac, with its
molecules, and intermolecular spaces running through the mass. In its case
space must be an insulator; for if it were a conductor it would resemble
'a fine metallic web,' penetrating the lac in every direction. But the
fact is that it resembles the wax of black sealing-wax, which surrounds
and insulates the particles of conducting carbon, interspersed throughout
its mass. In the case of shell-lac, therefore, space is an insulator.

But now, take the case of a conducting metal. Here we have, as before, the
swathing of space round every atom. If space be an insulator there can be
no transmission of electricity from atom to atom. But there is
transmission; hence space is a conductor. Thus he endeavours to hamper the
atomic theory. 'The reasoning,' he says, 'ends in a subversion of that
theory altogether; for if space be an insulator it cannot exist in
conducting bodies, and if it be a conductor it cannot exist in insulating
bodies. Any ground of reasoning,' he adds, as if carried away by the
ardour of argument, 'which tends to such conclusions as these must in
itself be false.'

He then tosses the atomic theory from horn to horn of his dilemmas. What
do we know, he asks, of the atom apart from its force? You imagine a
nucleus which may be called a, and surround it by forces which may be
called m; 'to my mind the a or nucleus vanishes, and the substance
consists in the powers of m. And indeed what notion can we form of the
nucleus independent of its powers? What thought remains on which to hang
the imagination of an a independent of the acknowledged forces?' Like
Boscovich, he abolishes the atom, and puts a 'centre of force' in its
place.

With his usual courage and sincerity he pushes his view to its utmost
consequences. 'This view of the constitution of matter,' he continues,
'would seem to involve necessarily the conclusion that matter fills all
space, or at least all space to which gravitation extends; for gravitation
is a property of matter dependent on a certain force, and it is this force
which constitutes the matter. In that view matter is not merely mutually
penetrable; (1) but each atom extends, so to say, throughout the whole of
the solar system, yet always retaining its own centre of force.'

It is the operation of a mind filled with thoughts of this profound,
strange, and subtle character that we have to take into account in dealing
with Faraday's later researches. A similar cast of thought pervades a
letter addressed by Faraday to Mr. Richard Phillips, and published in the
'Philosophical Magazine' for May, 1846. It is entitled 'Thoughts on
Ray-vibrations,' and it contains one of the most singular speculations
that ever emanated from a scientific mind. It must be remembered here,
that though Faraday lived amid such speculations he did not rate them
highly, and that he was prepared at any moment to change them or let them
go. They spurred him on, but they did not hamper him. His theoretic
notions were fluent; and when minds less plastic than his own attempted to
render those fluxional images rigid, he rebelled. He warns Phillips
moreover, that from first to last, 'he merely threw out as matter for
speculation the vague impressions of his mind; for he gave nothing as the
result of sufficient consideration, or as the settled conviction, or even
probable conclusion at which he had arrived.'

The gist of this communication is that gravitating force acts in lines
across space, and that the vibrations of light and radiant heat consist in
the tremors of these lines of force. 'This notion,' he says, 'as far as it
is admitted, will dispense with the ether, which, in another view is
supposed to be the medium in which these vibrations take place.' And he
adds further on, that his view 'endeavours to dismiss the ether but not
the vibrations.' The idea here set forth is the natural supplement of his
previous notion, that it is gravitating force which constitutes matter,
each atom extending, so to say, throughout the whole of the solar system.

The letter to Mr. Phillips winds up with this beautiful conclusion:—

'I think it likely that I have made many mistakes in the preceding pages,
for even to myself my ideas on this point appear only as the shadow of a
speculation, or as one of those impressions upon the mind which are
allowable for a time as guides to thought and research. He who labours in
experimental inquiries, knows how numerous these are, and how often their
apparent fitness and beauty vanish before the progress and development of
real natural truth.'

Let it then be remembered that Faraday entertained notions regarding
matter and force altogether distinct from the views generally held by
scientific men. Force seemed to him an entity dwelling along the line in
which it is exerted. The lines along which gravity acts between the sun
and earth seem figured in his mind as so many elastic strings; indeed he
accepts the assumed instantaneity of gravity as the expression of the
enormous elasticity of the 'lines of weight.' Such views, fruitful in the
case of magnetism, barren, as yet, in the case of gravity, explain his
efforts to transform this latter force. When he goes into the open air and
permits his helices to fall, to his mind's eye they are tearing through
the lines of gravitating power, and hence his hope and conviction that an
effect would and ought to be produced. It must ever be borne in mind that
Faraday's difficulty in dealing with these conceptions was at bottom the
same as that of Newton; that he is in fact trying to overleap this
difficulty, and with it probably the limits prescribed to the intellect
itself.

The idea of lines of magnetic force was suggested to Faraday by the linear
arrangement of iron filings when scattered over a magnet. He speaks of and
illustrates by sketches, the deflection, both convergent and divergent, of
the lines of force, when they pass respectively through magnetic and
diamagnetic bodies. These notions of concentration and divergence are also
based on the direct observation of his filings. So long did he brood upon
these lines; so habitually did he associate them with his experiments on
induced currents, that the association became 'indissoluble,' and he could
not think without them. 'I have been so accustomed,' he writes, 'to employ
them, and especially in my last researches, that I may have unwittingly
become prejudiced in their favour, and ceased to be a clear-sighted judge.
Still, I have always endeavoured to make experiment the test and
controller of theory and opinion; but neither by that nor by close
cross-examination in principle, have I been made aware of any error
involved in their use.'

In his later researches on magne-crystallic action, the idea of lines of
force is extensively employed; it indeed led him to an experiment which
lies at the root of the whole question. In his subsequent researches on
Atmospheric Magnetism the idea receives still wider application, showing
itself to be wonderfully flexible and convenient. Indeed without this
conception the attempt to seize upon the magnetic actions, possible or
actual, of the atmosphere would be difficult in the extreme; but the
notion of lines of force, and of their divergence and convergence, guides
Faraday without perplexity through all the intricacies of the question.
After the completion of those researches, and in a paper forwarded to the
Royal Society on October 22, 1851, he devotes himself to the formal
development and illustration of his favourite idea. The paper bears the
title, 'On lines of magnetic force, their definite character, and their
distribution within a magnet and through space.' A deep reflectiveness is
the characteristic of this memoir. In his experiments, which are perfectly
beautiful and profoundly suggestive, he takes but a secondary delight. His
object is to illustrate the utility of his conception of lines of force.
'The study of these lines,' he says, 'has at different times been greatly
influential in leading me to various results which I think prove their
utility as well as fertility.'

Faraday for a long period used the lines of force merely as 'a
representative idea.' He seemed for a time averse to going further in
expression than the lines themselves, however much further he may have
gone in idea. That he believed them to exist at all times round a magnet,
and irrespective of the existence of magnetic matter, such as iron
filings, external to the magnet, is certain. No doubt the space round
every magnet presented itself to his imagination as traversed by loops of
magnetic power; but he was chary in speaking of the physical substratum of
those loops. Indeed it may be doubted whether the physical theory of lines
of force presented itself with any distinctness to his own mind. The
possible complicity of the luminiferous ether in magnetic phenomena was
certainly in his thoughts. 'How the magnetic force,' he writes, 'is
transferred through bodies or through space we know not; whether the
result is merely action at a distance, as in the case of gravity; or by
some intermediate agency, as in the case of light, heat, the electric
current, and (as I believe) static electric action. The idea of magnetic
fluids, as applied by some, or of Magnetic centres of action, does not
include that of the latter kind of transmission, but the idea of lines of
force does.' And he continues thus:—'I am more inclined to the
notion that in the transmission of the (magnetic) force there is such an
action (an intermediate agency) external to the magnet, than that the
effects are merely attraction and repulsion at a distance. Such an
affection may be a function of the ether; for it is not at all unlikely
that, if there be an ether, it should have other uses than simply the
conveyance of radiations.' When he speaks of the magnet in certain cases,
'revolving amongst its own forces,' he appears to have some conception of
this kind in view.

A great part of the investigation completed in October, 1851, was taken up
with the motions of wires round the poles of a magnet and the converse. He
carried an insulated wire along the axis of a bar magnet from its pole to
its equator, where it issued from the magnet, and was bent up so as to
connect its two ends. A complete circuit, no part of which was in contact
with the magnet, was thus obtained. He found that when the magnet and the
external wire were rotated together no current was produced; whereas, when
either of them was rotated and the other left at rest currents were
evolved. He then abandoned the axial wire, and allowed the magnet itself
to take its place; the result was the same. (2) It was the relative motion
of the magnet and the loop that was effectual in producing a current.

The lines of force have their roots in the magnet, and though they may
expand into infinite space, they eventually return to the magnet. Now
these lines may be intersected close to the magnet or at a distance from
it. Faraday finds distance to be perfectly immaterial so long as the
number of lines intersected is the same. For example, when the loop
connecting the equator and the pole of his barmagnet performs one complete
revolution round the magnet, it is manifest that all the lines of force
issuing from the magnet are once intersected. Now it matters not whether
the loop be ten feet or ten inches in length, it matters not how it may be
twisted and contorted, it matters not how near to the magnet or how
distant from it the loop may be, one revolution always produces the same
amount of current electricity, because in all these cases all the lines of
force issuing from the magnet are once intersected and no more.

From the external portion of the circuit he passes in idea to the
internal, and follows the lines of force into the body of the magnet
itself. His conclusion is that there exist lines of force within the
magnet of the same nature as those without. What is more, they are exactly
equal in amount to those without. They have a relation in direction to
those without; and in fact are continuations of them.... 'Every line of
force, therefore, at whatever distance it may be taken from the magnet,
must be considered as a closed circuit, passing in some part of its course
through the magnet, and having an equal amount of force in every part of
its course.'

All the results here described were obtained with moving metals. 'But,' he
continues with profound sagacity, 'mere motion would not generate a
relation, which had not a foundation in the existence of some previous
state; and therefore the quiescent metals must be in some relation to the
active centre of force,' that is to the magnet. He here touches the core
of the whole question, and when we can state the condition into which the
conducting wire is thrown before it is moved, we shall then be in a
position to understand the physical constitution of the electric current
generated by its motion.

In this inquiry Faraday worked with steel magnets, the force of which
varies with the distance from the magnet. He then sought a uniform field
of magnetic force, and found it in space as affected by the magnetism of
the earth. His next memoir, sent to the Royal Society, December 31, 1851,
is 'on the employment of the Induced Magnetoelectro Current as a test and
measure of magnetic forces.' He forms rectangles and rings, and by
ingenious and simple devices collects the opposed currents which are
developed in them by rotation across the terrestrial lines of magnetic
force. He varies the shapes of his rectangles while preserving their areas
constant, and finds that the constant area produces always the same amount
of current per revolution. The current depends solely on the number of
lines of force intersected, and when this number is kept constant the
current remains constant too. Thus the lines of magnetic force are
continually before his eyes, by their aid he colligates his facts, and
through the inspirations derived from them he vastly expands the
boundaries of our experimental knowledge. The beauty and exactitude of the
results of this investigation are extraordinary. I cannot help thinking
while I dwell upon them, that this discovery of magneto-electricity is the
greatest experimental result ever obtained by an investigator. It is the
Mont Blanc of Faraday's own achievements. He always worked at great
elevations, but a higher than this he never subsequently attained.

Footnotes to Chapter 13

(1) He compares the interpenetration of two atoms to the
coalescence of two distinct waves, which though for a moment
blended to a single mass, preserve their individuality, and
afterwards separate.
(2) In this form the experiment is identical with one made
twenty years earlier. See page 34.

Chapter 14.

Unity and convertibility of natural forces: theory of the
electric current.

The terms unity and convertibility, as applied to natural forces, are
often employed in these investigations, many profound and beautiful
thoughts respecting these subjects being expressed in Faraday's memoirs.
Modern inquiry has, however, much augmented our knowledge of the
relationship of natural forces, and it seems worth while to say a few
words here, tending to clear up certain misconceptions which appear to
exist among philosophic writers regarding this relationship.

The whole stock of energy or working-power in the world consists of
attractions, repulsions, and motions. If the attractions and repulsions
are so circumstanced as to be able to produce motion, they are sources of
working-power, but not otherwise. Let us for the sake of simplicity
confine our attention to the case of attraction. The attraction exerted
between the earth and a body at a distance from the earth's surface is a
source of working-power; because the body can be moved by the attraction,
and in falling to the earth can perform work. When it rests upon the
earth's surface it is not a source of power or energy, because it can fall
no further. But though it has ceased to be a source of energy, the
attraction of gravity still acts as a force, which holds the earth and
weight together.

The same remarks apply to attracting atoms and molecules. As long as
distance separates them, they can move across it in obedience to the
attraction, and the motion thus produced may, by proper appliances, be
caused to perform mechanical work. When, for example, two atoms of
hydrogen unite with one of oxygen, to form water the atoms are first drawn
towards each other—they move, they clash, and then by virtue of
their resiliency, they recoil and quiver. To this quivering motion we give
the name of heat. Now this quivering motion is merely the redistribution
of the motion produced by the chemical affinity; and this is the only
sense in which chemical affinity can be said to be converted into heat. We
must not imagine the chemical attraction destroyed, or converted into
anything else. For the atoms, when mutually clasped to form a molecule of
water, are held together by the very attraction which first drew them
towards each other. That which has really been expended is the pull
exerted through the space by which the distance between the atoms has been
diminished.

If this be understood, it will be at once seen that gravity may in this
sense be said to be convertible into heat; that it is in reality no more
an outstanding and inconvertible agent, as it is sometimes stated to be,
than chemical affinity. By the exertion of a certain pull, through a
certain space, a body is caused to clash with a certain definite velocity
against the earth. Heat is thereby developed, and this is the only sense
in which gravity can be said to be converted into heat. In no case is the
force which produces the motion annihilated or changed into anything else.
The mutual attraction of the earth and weight exists when they are in
contact as when they were separate; but the ability of that attraction to
employ itself in the production of motion does not exist.

The transformation, in this case, is easily followed by the mind's eye.
First, the weight as a whole is set in motion by the attraction of
gravity. This motion of the mass is arrested by collision with the earth;
being broken up into molecular tremors, to which we give the name of heat.

And when we reverse the process, and employ those tremors of heat to raise
a weight, as is done through the intermediation of an elastic fluid in the
steam-engine, a certain definite portion of the molecular motion is
destroyed in raising the weight. In this sense, and this sense only, can
the heat be said to be converted into gravity, or more correctly, into
potential energy of gravity. It is not that the destruction of the heat
has created any new attraction, but simply that the old attraction has now
a power conferred upon it, of exerting a certain definite pull in the
interval between the starting-point of the falling weight and its
collision with the earth.

So also as regards magnetic attraction: when a sphere of iron placed at
some distance from a magnet rushes towards the magnet, and has its motion
stopped by collision, an effect mechanically the same as that produced by
the attraction of gravity occurs. The magnetic attraction generates the
motion of the mass, and the stoppage of that motion produces heat. In this
sense, and in this sense only, is there a transformation of magnetic work
into heat. And if by the mechanical action of heat, brought to bear by
means of a suitable machine, the sphere be torn from the magnet and again
placed at a distance, a power of exerting a pull through that distance,
and producing a new motion of the sphere, is thereby conferred upon the
magnet; in this sense, and in this sense only, is the heat converted into
magnetic potential energy.

When, therefore, writers on the conservation of energy speak of tensions
being 'consumed' and 'generated,' they do not mean thereby that old
attractions have been annihilated and new ones brought into existence, but
that, in the one case, the power of the attraction to produce motion has
been diminished by the shortening of the distance between the attracting
bodies, and that in the other case the power of producing motion has been
augmented by the increase of the distance. These remarks apply to all
bodies, whether they be sensible masses or molecules.

Of the inner quality that enables matter to attract matter we know
nothing; and the law of conservation makes no statement regarding that
quality. It takes the facts of attraction as they stand, and affirms only
the constancy of working-power. That power may exist in the form of
MOTION; or it may exist in the form of FORCE, with distance to act
through. The former is dynamic energy, the latter is potential energy, the
constancy of the sum of both being affirmed by the law of conservation.
The convertibility of natural forces consists solely in transformations of
dynamic into potential, and of potential into dynamic, energy, which are
incessantly going on. In no other sense has the convertibility of force,
at present, any scientific meaning.

By the contraction of a muscle a man lifts a weight from the earth. But
the muscle can contract only through the oxidation of its own tissue or of
the blood passing through it. Molecular motion is thus converted into
mechanical motion. Supposing the muscle to contract without raising the
weight, oxidation would also occur, but the whole of the heat produced by
this oxidation would be liberated in the muscle itself. Not so when it
performs external work; to do that work a certain definite portion of the
heat of oxidation must be expended. It is so expended in pulling the
weight away from the earth. If the weight be permitted to fall, the heat
generated by its collision with the earth would exactly make up for that
lacking in the muscle during the lifting of the weight. In the case here
supposed, we have a conversion of molecular muscular action into potential
energy of gravity; and a conversion of that potential energy into heat;
the heat, however, appearing at a distance from its real origin in the
muscle. The whole process consists of a transference of molecular motion
from the muscle to the weight, and gravitating force is the mere
go-between, by means of which the transference is effected.

These considerations will help to clear our way to the conception of the
transformations which occur when a wire is moved across the lines of force
in a magnetic field. In this case it is commonly said we have a conversion
of magnetism into electricity. But let us endeavour to understand what
really occurs. For the sake of simplicity, and with a view to its
translation into a different one subsequently, let us adopt for a moment
the provisional conception of a mixed fluid in the wire, composed of
positive and negative electricities in equal quantities, and therefore
perfectly neutralizing each other when the wire is still. By the motion of
the wire, say with the hand, towards the magnet, what the Germans call a
Scheidungs-Kraft—a separating force—is brought into play. This
force tears the mixed fluids asunder, and drives them in two currents, the
one positive and the other negative, in two opposite directions through
the wire. The presence of these currents evokes a force of repulsion
between the magnet and the wire; and to cause the one to approach the
other, this repulsion must be overcome. The overcoming of this repulsion
is, in fact, the work done in separating and impelling the two
electricities. When the wire is moved away from the magnet, a
Scheidungs-Kraft, or separating force, also comes into play; but now it is
an attraction that has to be surmounted. In surmounting it, currents are
developed in directions opposed to the former; positive takes the place of
negative, and negative the place of positive; the overcoming of the
attraction being the work done in separating and impelling the two
electricities.

The mechanical action occurring here is different from that occurring
where a sphere of soft iron is withdrawn from a magnet, and again
attracted. In this case muscular force is expended during the act of
separation; but the attraction of the magnet effects the reunion. In the
case of the moving wire also we overcome a resistance in separating it
from the magnet, and thus far the action is mechanically the same as the
separation of the sphere of iron. But after the wire has ceased moving,
the attraction ceases; and so far from any action occurring similar to
that which draws the iron sphere back to the magnet, we have to overcome a
repulsion to bring them together.

There is no potential energy conferred either by the removal or by the
approach of the wire, and the only power really transformed or converted,
in the experiment, is muscular power. Nothing that could in strictness be
called a conversion of magnetism into electricity occurs. The muscular
oxidation that moves the wire fails to produce within the muscle its due
amount of heat, a portion of that heat, equivalent to the resistance
overcome, appearing in the moving wire instead.

Is this effect an attraction and a repulsion at a distance? If so, why
should both cease when the wire ceases to move? In fact, the deportment of
the wire resembles far more that of a body moving in a resisting medium
than anything else; the resistance ceasing when the motion is suspended.
Let us imagine the case of a liquid so mobile that the hand may be passed
through it to and fro, without encountering any sensible resistance. It
resembles the motion of a conductor in the unexcited field of an
electro-magnet. Now, let us suppose a body placed in the liquid, or acting
on it, which confers upon it the property of viscosity; the hand would no
longer move freely. During its motion, but then only, resistance would be
encountered and overcome. Here we have rudely represented the case of the
excited magnetic field, and the result in both cases would be
substantially the same. In both cases heat would, in the end, be generated
outside of the muscle, its amount being exactly equivalent to the
resistance overcome.

Let us push the analogy a little further; suppose in the case of the fluid
rendered viscous, as assumed a moment ago, the viscosity not to be so
great as to prevent the formation of ripples when the hand is passed
through the liquid. Then the motion of the hand, before its final
conversion into heat, would exist for a time as wave-motion, which, on
subsiding, would generate its due equivalent of heat. This intermediate
stage, in the case of our moving wire, is represented by the period during
which the electric current is flowing through it; but that current, like
the ripples of our liquid, soon subsides, being, like them, converted into
heat.

Do these words shadow forth anything like the reality? Such speculations
cannot be injurious if they are enunciated without dogmatism. I do confess
that ideas such as these here indicated exercise a strong fascination on
my mind. Is then the magnetic field really viscous, and if so, what
substance exists in it and the wire to produce the viscosity? Let us first
look at the proved effects, and afterwards turn our thoughts back upon
their cause. When the wire approaches the magnet, an action is evoked
within it, which travels through it with a velocity comparable to that of
light. One substance only in the universe has been hitherto proved
competent to transmit power at this velocity; the luminiferous ether. Not
only its rapidity of progression, but its ability to produce the motion of
light and heat, indicates that the electric current is also motion. (1)
Further, there is a striking resemblance between the action of good and
bad conductors as regards electricity, and the action of diathermanous and
adiathermanous bodies as regards radiant heat. The good conductor is
diathermanous to the electric current; it allows free transmission without
the development of heat. The bad conductor is adiathermanous to the
electric current, and hence the passage of the latter is accompanied by
the development of heat. I am strongly inclined to hold the electric
current, pure and simple, to be a motion of the ether alone; good
conductors being so constituted that the motion may be propagated through
their ether without sensible transfer to their atoms, while in the case of
bad conductors this transfer is effected, the transferred motion appearing
as heat. (2)

I do not know whether Faraday would have subscribed to what is here
written; probably his habitual caution would have prevented him from
committing himself to anything so definite. But some such idea filled his
mind and coloured his language through all the later years of his life. I
dare not say that he has been always successful in the treatment of these
theoretic notions. In his speculations he mixes together light and
darkness in varying proportions, and carries us along with him through
strong alternations of both. It is impossible to say how a certain amount
of mathematical training would have affected his work. We cannot say what
its influence would have been upon that force of inspiration that urged
him on; whether it would have daunted him, and prevented him from driving
his adits into places where no theory pointed to a lode. If so, then we
may rejoice that this strong delver at the mine of natural knowledge was
left free to wield his mattock in his own way. It must be admitted, that
Faraday's purely speculative writings often lack that precision which the
mathematical habit of thought confers. Still across them flash frequent
gleams of prescient wisdom which will excite admiration throughout all
time; while the facts, relations, principles, and laws which his
experiments have established are sure to form the body of grand theories
yet to come.

Footnotes to Chapter 14

(1) Mr. Clerk Maxwell has recently published an exceedingly
important investigation connected with this question. Even
in the non-mathematical portions of the memoirs of Mr.
Maxwell, the admirable spirit of his philosophy is
sufficiently revealed. As regards the employment of
scientific imagery, I hardly know his equal in power of
conception and clearness of definition.
(2) One important difference, of course, exists between the
effect of motion in the magnetic field, and motion in a
resisting medium. In the former case the heat is generated
in the moving conductor, in the latter it is in part
generated in the medium.

Chapter 15.

Summary.

When from an Alpine height the eye of the climber ranges over the
mountains, he finds that for the most part they resolve themselves into
distinct groups, each consisting of a dominant mass surrounded by peaks of
lesser elevation. The power which lifted the mightier eminences, in nearly
all cases lifted others to an almost equal height. And so it is with the
discoveries of Faraday. As a general rule, the dominant result does not
stand alone, but forms the culminating point of a vast and varied mass of
inquiry. In this way, round about his great discovery of Magneto-electric
Induction, other weighty labours group themselves. His investigations on
the Extra Current; on the Polar and other Condition of Diamagnetic Bodies;
on Lines of Magnetic Force, their definite character and distribution; on
the employment of the Induced Magneto-electric Current as a measure and
test of Magnetic Action; on the Revulsive Phenomena of the magnetic field,
are all, notwithstanding the diversity of title, researches in the domain
of Magneto-electric Induction.

Faraday's second group of researches and discoveries embrace the chemical
phenomena of the current. The dominant result here is the great law of
definite Electro-chemical Decomposition, around which are massed various
researches on Electro-chemical Conduction and on Electrolysis both with
the Machine and with the Pile. To this group also belongs his analysis of
the Contact Theory, his inquiries as to the Source of Voltaic Electricity,
and his final development of the Chemical Theory of the pile.

His third great discovery is the Magnetization of Light, which I should
liken to the Weisshorn among mountains—high, beautiful, and alone.

The dominant result of his fourth group of researches is the discovery of
Diamagnetism, announced in his memoir as the Magnetic Condition of all
Matter, round which are grouped his inquiries on the Magnetism of Flame
and Gases; on Magne-crystallic action, and on Atmospheric Magnetism, in
its relations to the annual and diurnal variation of the needle, the full
significance of which is still to be shown.

These are Faraday's most massive discoveries, and upon them his fame must
mainly rest. But even without them, sufficient would remain to secure for
him a high and lasting scientific reputation. We should still have his
researches on the Liquefaction of Gases; on Frictional Electricity; on the
Electricity of the Gymnotus; on the source of Power in the Hydro-electric
machine, the last two investigations being untouched in the foregoing
memoir; on Electro-magnetic Rotations; on Regelation; all his more purely
Chemical Researches, including his discovery of Benzol. Besides these he
published a multitude of minor papers, most of which, in some way or
other, illustrate his genius. I have made no allusion to his power and
sweetness as a lecturer. Taking him for all in all, I think it will be
conceded that Michael Faraday was the greatest experimental philosopher
the world has ever seen; and I will add the opinion, that the progress of
future research will tend, not to dim or to diminish, but to enhance and
glorify the labours of this mighty investigator.

Chapter 16.

Illustrations of Character.

Thus far I have confined myself to topics mainly interesting to the man of
science, endeavouring, however, to treat them in a manner unrepellent to
the general reader who might wish to obtain a notion of Faraday as a
worker. On others will fall the duty of presenting to the world a picture
of the man. But I know you will permit me to add to the foregoing analysis
a few personal reminiscences and remarks, tending to connect Faraday with
a wider world than that of science—namely, with the general human
heart.

One word in reference to his married life, in addition to what has been
already said, may find a place here. As in the former case, Faraday shall
be his own spokesman. The following paragraph, though written in the third
person, is from his hand:—'On June 12, 1821, he married, an event
which more than any other contributed to his earthly happiness and
healthful state of mind. The union has continued for twenty-eight years
and has in no wise changed, except in the depth and strength of its
character.'

Faraday's immediate forefathers lived in a little place called Clapham
Wood Hall, in Yorkshire. Here dwelt Robert Faraday and Elizabeth his wife,
who had ten children, one of them, James Faraday, born in 1761, being
father to the philosopher. A family tradition exists that the Faradays
came originally from Ireland. Faraday himself has more than once expressed
to me his belief that his blood was in part Celtic, but how much of it was
so, or when the infusion took place, he was unable to say. He could
imitate the Irish brogue, and his wonderful vivacity may have been in part
due to his extraction. But there were other qualities which we should
hardly think of deriving from Ireland. The most prominent of these was his
sense of order, which ran like a luminous beam through all the
transactions of his life. The most entangled and complicated matters fell
into harmony in his hands. His mode of keeping accounts excited the
admiration of the managing board of this Institution. And his science was
similarly ordered. In his Experimental Researches, he numbered every
paragraph, and welded their various parts together by incessant reference.
His private notes of the Experimental Researches, which are happily
preserved, are similarly numbered: their last paragraph bears the figure
16,041. His working qualities, moreover, showed the tenacity of the
Teuton. His nature was impulsive, but there was a force behind the impulse
which did not permit it to retreat. If in his warm moments he formed a
resolution, in his cool ones he made that resolution good. Thus his fire
was that of a solid combustible, not that of a gas, which blazes suddenly,
and dies as suddenly away.

And here I must claim your tolerance for the limits by which I am
confined. No materials for a life of Faraday are in my hands, and what I
have now to say has arisen almost wholly out of our close personal
relationship.

Letters of his, covering a period of sixteen years, are before me, each
one of which contains some characteristic utterance;—strong, yet
delicate in counsel, joyful in encouragement, and warm in affection.
References which would be pleasant to such of them as still live are made
to Humboldt, Biot, Dumas, Chevreul, Magnus, and Arago. Accident brought
these names prominently forward; but many others would be required to
complete his list of continental friends. He prized the love and sympathy
of men—prized it almost more than the renown which his science
brought him. Nearly a dozen years ago it fell to my lot to write a review
of his 'Experimental Researches' for the 'Philosophical Magazine.' After
he had read it, he took me by the hand, and said, 'Tyndall, the sweetest
reward of my work is the sympathy and good will which it has caused to
flow in upon me from all quarters of the world.' Among his letters I find
little sparks of kindness, precious to no one but myself, but more
precious to me than all. He would peep into the laboratory when he thought
me weary, and take me upstairs with him to rest. And if I happened to be
absent, he would leave a little note for me, couched in this or some other
similar form:—'Dear Tyndall,—I was looking for you, because we
were at tea—we have not yet done—will you come up?' I
frequently shared his early dinner; almost always, in fact, while my
lectures were going on. There was no trace of asceticism in his nature. He
preferred the meat and wine of life to its locusts and wild honey. Never
once during an intimacy of fifteen years did he mention religion to me,
save when I drew him on to the subject. He then spoke to me without
hesitation or reluctance; not with any apparent desire to 'improve the
occasion,' but to give me such information as I sought. He believed the
human heart to be swayed by a power to which science or logic opened no
approach, and, right or wrong, this faith, held in perfect tolerance of
the faiths of others, strengthened and beautified his life.

From the letters just referred to, I will select three for publication
here. I choose the first, because it contains a passage revealing the
feelings with which Faraday regarded his vocation, and also because it
contains an allusion which will give pleasure to a friend.

'Royal Institution. ( this is crossed out by Faraday )

'Ventnor, Isle of Wight, June 28, 1854.

'My Dear Tyndall,—You see by the top of this letter how much habit
prevails over me; I have just read yours from thence, and yet I think
myself there. However, I have left its science in very good keeping, and I
am glad to learn that you are at experiment once more. But how is the
health? Not well, I fear. I wish you would get yourself strong first and
work afterwards. As for the fruits, I am sure they will be good, for
though I sometimes despond as regards myself, I do not as regards you. You
are young, I am old.... But then our subjects are so glorious, that to
work at them rejoices and encourages the feeblest; delights and enchants
the strongest.

'I have not yet seen anything from Magnus. Thoughts of him always delight
me. We shall look at his black sulphur together. I heard from Schonbein
the other day. He tells me that Liebig is full of ozone, i.e., of
allotropic oxygen.

'Good-bye for the present.

'Ever, my dear Tyndall,

'Yours truly,

'M. Faraday.'

The contemplation of Nature, and his own relation to her, produced in
Faraday a kind of spiritual exaltation which makes itself manifest here.
His religious feeling and his philosophy could not be kept apart; there
was an habitual overflow of the one into the other.

Whether he or another was its exponent, he appeared to take equal delight
in science. A good experiment would make him almost dance with delight. In
November, 1850, he wrote to me thus:—'I hope some day to take up the
point respecting the magnetism of associated particles. In the meantime I
rejoice at every addition to the facts and reasoning connected with the
subject. When science is a republic, then it gains: and though I am no
republican in other matters, I am in that.' All his letters illustrate
this catholicity of feeling. Ten years ago, when going down to Brighton,
he carried with him a little paper I had just completed, and afterwards
wrote to me. His letter is a mere sample of the sympathy which he always
showed to me and my work.

'Brighton, December 9, 1857.

'My Dear Tyndall,—I cannot resist the pleasure of saying how very
much I have enjoyed your paper. Every part has given me delight. It goes
on from point to point beautifully. You will find many pencil marks, for I
made them as I read. I let them stand, for though many of them receive
their answer as the story proceeds, yet they show how the wording
impresses a mind fresh to the subject, and perhaps here and there you may
like to alter it slightly, if you wish the full idea, i.e., not an
inaccurate one, to be suggested at first; and yet after all I believe it
is not your exposition, but the natural jumping to a conclusion that
affects or has affected my pencil.

'We return on Friday, when I will return you the paper.

'Ever truly yours,

'M. Faraday.'

The third letter will come in its proper place towards the end.

While once conversing with Faraday on science, in its relations to
commerce and litigation, he said to me, that at a certain period of his
career, he was forced definitely to ask himself, and finally to decide
whether he should make wealth or science the pursuit of his life. He could
not serve both masters, and he was therefore compelled to choose between
them. After the discovery of magneto-electricity his fame was so noised
abroad, that the commercial world would hardly have considered any
remuneration too high for the aid of abilities like his. Even before he
became so famous, he had done a little 'professional business.' This was
the phrase he applied to his purely commercial work. His friend, Richard
Phillips, for example, had induced him to undertake a number of analyses,
which produced, in the year 1830, an addition to his income of more than a
thousand pounds; and in 1831 a still greater addition. He had only to will
it to raise in 1832 his professional business income to 5000L. a year.
Indeed double this sum would be a wholly insufficient estimate of what he
might, with ease, have realised annually during the last thirty years of
his life.

While restudying the Experimental Researches with reference to the present
memoir, the conversation with Faraday here alluded to came to my
recollection, and I sought to ascertain the period when the question,
'wealth or science,' had presented itself with such emphasis to his mind.
I fixed upon the year 1831 or 1832, for it seemed beyond the range of
human power to pursue science as he had done during the subsequent years,
and to pursue commercial work at the same time. To test this conclusion I
asked permission to see his accounts, and on my own responsibility, I will
state the result. In 1832, his professional business income, instead of
rising to 5000L., or more, fell from 1090L. 4s. to 155L. 9s. From this it
fell with slight oscillations to 92L. in 1837, and to zero in 1838.
Between 1839 and 1845, it never, except in one instance, exceeded 22L.;
being for the most part much under this. The exceptional year referred to
was that in which he and Sir Charles Lyell were engaged by Government to
write a report on the Haswell Colliery explosion, and then his business
income rose to 112L. From the end of 1845 to the day of his death,
Faraday's annual professional business income was exactly zero. Taking the
duration of his life into account, this son of a blacksmith, and
apprentice to a bookbinder, had to decide between a fortune of 150,000L.
on the one side, and his undowered science on the other. He chose the
latter, and died a poor man. But his was the glory of holding aloft among
the nations the scientific name of England for a period of forty years.

The outward and visible signs of fame were also of less account to him
than to most men. He had been loaded with scientific honours from all
parts of the world. Without, I imagine, a dissentient voice, he was
regarded as the prince of the physical investigators of the present age.
The highest scientific position in this country he had, however, never
filled. When the late excellent and lamented Lord Wrottesley resigned the
presidency of the Royal Society, a deputation from the council, consisting
of his Lordship, Mr. Grove, and Mr. Gassiot, waited upon Faraday, to urge
him to accept the president's chair. All that argument or friendly
persuasion could do was done to induce him to yield to the wishes of the
council, which was also the unanimous wish of scientific men. A knowledge
of the quickness of his own nature had induced in Faraday the habit of
requiring an interval of reflection, before he decided upon any question
of importance. In the present instance he followed his usual habit, and
begged for a little time.

On the following morning, I went up to his room and said on entering that
I had come to him with some anxiety of mind. He demanded its cause, and I
responded:—'Lest you should have decided against the wishes of the
deputation that waited on you yesterday.' 'You would not urge me to
undertake this responsibility,' he said. 'I not only urge you,' was my
reply, 'but I consider it your bounden duty to accept it.' He spoke of the
labour that it would involve; urged that it was not in his nature to take
things easy; and that if he became president, he would surely have to stir
many new questions, and agitate for some changes. I said that in such
cases he would find himself supported by the youth and strength of the
Royal Society. This, however, did not seem to satisfy him. Mrs. Faraday
came into the room, and he appealed to her. Her decision was adverse, and
I deprecated her decision. 'Tyndall,' he said at length, 'I must remain
plain Michael Faraday to the last; and let me now tell you, that if I
accepted the honour which the Royal Society desires to confer upon me, I
would not answer for the integrity of my intellect for a single year.' I
urged him no more, and Lord Wrottesley had a most worthy successor in Sir
Benjamin Brodie.

After the death of the Duke of Northumberland, our Board of Managers
wished to see Mr. Faraday finish his career as President of the
Institution, which he had entered on weekly wages more than half a century
before. But he would have nothing to do with the presidency. He wished for
rest, and the reverent affection of his friends was to him infinitely more
precious than all the honours of official life.

The first requisite of the intellectual life of Faraday was the
independence of his mind; and though prompt to urge obedience where
obedience was due, with every right assertion of manhood he intensely
sympathized. Even rashness on the side of honour found from him ready
forgiveness, if not open applause. The wisdom of years, tempered by a
character of this kind, rendered his counsel peculiarly precious to men
sensitive like himself. I often sought that counsel, and, with your
permission, will illustrate its character by one or two typical instances.

In 1855, I was appointed examiner under the Council for Military
Education. At that time, as indeed now, I entertained strong convictions
as to the enormous utility of physical science to officers of artillery
and engineers, and whenever opportunity offered, I expressed this
conviction without reserve. I did not think the recognition, though
considerable, accorded to physical science in those examinations at all
proportionate to its importance; and this probably rendered me more
jealous than I otherwise should have been of its claims.

In Trinity College, Dublin, a school had been organized with reference to
the Woolwich examinations, and a large number of exceedingly
well-instructed young gentlemen were sent over from Dublin, to compete for
appointments in the artillery and the engineers. The result of one
examination was particularly satisfactory to me; indeed the marks obtained
appeared so eloquent that I forbore saying a word about them. My
colleagues, however, followed the usual custom of sending in brief reports
with their returns of marks. After the results were published, a leading
article appeared in 'The Times,' in which the reports were largely quoted,
praise being bestowed on all the candidates, except the excellent young
fellows who had passed through my hands.

A letter from Trinity College drew my attention to this article, bitterly
complaining that whereas the marks proved them to be the best of all, the
science candidates were wholly ignored. I tried to set matters right by
publishing, on my own responsibility, a letter in 'The Times.' The act, I
knew, could not bear justification from the War Office point of view; and
I expected and risked the displeasure of my superiors. The merited
reprimand promptly came. 'Highly as the Secretary of State for War might
value the expression of Professor Tyndall's opinion, he begged to say that
an examiner, appointed by His Royal Highness the Commander-in-Chief, had
no right to appear in the public papers as Professor Tyndall has done,
without the sanction of the War Office.' Nothing could be more just than
this reproof, but I did not like to rest under it. I wrote a reply, and
previous to sending it took it up to Faraday. We sat together before his
fire, and he looked very earnest as he rubbed his hands and pondered. The
following conversation then passed between us:—

F. You certainly have received a reprimand, Tyndall; but the matter is
over, and if you wish to accept the reproof, you will hear no more about
it.

T. But I do not wish to accept it.

F. Then you know what the consequence of sending that letter will be?

T. I do.

F. They will dismiss you.

T. I know it.

F. Then send the letter!

The letter was firm, but respectful; it acknowledged the justice of the
censure, but expressed neither repentance nor regret. Faraday, in his
gracious way, slightly altered a sentence or two to make it more
respectful still. It was duly sent, and on the following day I entered the
Institution with the conviction that my dismissal was there before me.
Weeks, however, passed. At length the well-known envelope appeared, and I
broke the seal, not doubting the contents. They were very different from
what I expected. 'The Secretary of State for War has received Professor
Tyndall's letter, and deems the explanation therein given perfectly
satisfactory.' I have often wished for an opportunity of publicly
acknowledging this liberal treatment, proving, as it did, that Lord
Panmure could discern and make allowance for a good intention, though it
involved an offence against routine. For many years subsequently it was my
privilege to act under that excellent body, the Council for Military
Education.

On another occasion of this kind, having encouraged me in a somewhat hardy
resolution I had formed, Faraday backed his encouragement by an
illustration drawn from his own life. The subject will interest you, and
it is so sure to be talked about in the world, that no avoidable harm can
rise from its introduction here.

In the year 1835, Sir Robert Peel wished to offer Faraday a pension, but
that great statesman quitted office before he was able to realise his
wish. The Minister who founded these pensions intended them, I believe, to
be marks of honour which even proud men might accept without compromise of
independence. When, however, the intimation first reached Faraday in an
unofficial way, he wrote a letter announcing his determination to decline
the pension; and stating that he was quite competent to earn his
livelihood himself. That letter still exists, but it was never sent,
Faraday's repugnance having been overruled by his friends. When Lord
Melbourne came into office, he desired to see Faraday; and probably in
utter ignorance of the man—for unhappily for them and us, Ministers
of State in England are only too often ignorant of great Englishmen—his
Lordship said something that must have deeply displeased his visitor. All
the circumstances were once communicated to me, but I have forgotten the
details. The term 'humbug,' I think, was incautiously employed by his
Lordship, and other expressions were used of a similar kind. Faraday
quitted the Minister with his own resolves, and that evening he left his
card and a short and decisive note at the residence of Lord Melbourne,
stating that he had manifestly mistaken his Lordship's intention of
honouring science in his person, and declining to have anything whatever
to do with the proposed pension. The good-humoured nobleman at first
considered the matter a capital joke; but he was afterwards led to look at
it more seriously. An excellent lady, who was a friend both to Faraday and
the Minister, tried to arrange matters between them; but she found Faraday
very difficult to move from the position he had assumed. After many
fruitless efforts, she at length begged of him to state what he would
require of Lord Melbourne to induce him to change his mind. He replied, 'I
should require from his Lordship what I have no right or reason to expect
that he would grant—a written apology for the words he permitted
himself to use to me.' The required apology came, frank and full,
creditable, I thought, alike to the Prime Minister and the philosopher.

Considering the enormous strain imposed on Faraday's intellect, the
boy-like buoyancy even of his later years was astonishing. He was often
prostrate, but he had immense resiliency, which he brought into action by
getting away from London whenever his health failed. I have already
indicated the thoughts which filled his mind during the evening of his
life. He brooded on magnetic media and lines of force; and the great
object of the last investigation he ever undertook was the decision of the
question whether magnetic force requires time for its propagation. How he
proposed to attack this subject we may never know. But he has left some
beautiful apparatus behind; delicate wheels and pinions, and associated
mirrors, which were to have been employed in the investigation. The mere
conception of such an inquiry is an illustration of his strength and
hopefulness, and it is impossible to say to what results it might have led
him. But the work was too heavy for his tired brain. It was long before he
could bring himself to relinquish it and during this struggle he often
suffered from fatigue of mind. It was at this period, and before he
resigned himself to the repose which marked the last two years of his
life, that he wrote to me the following letter—one of many priceless
letters now before me—which reveals, more than anything another pen
could express, the state of his mind at the time. I was sometimes censured
in his presence for my doings in the Alps, but his constant reply was,
'Let him alone, he knows how to take care of himself.' In this letter,
anxiety on this score reveals itself for the first time.

'Hampton Court, August 1, 1864.

'My Dear Tyndall,—I do not know whether my letter will catch you,
but I will risk it, though feeling very unfit to communicate with a man
whose life is as vivid and active as yours; but the receipt of your kind
letter makes me to know that, though I forget, I am not forgotten, and
though I am not able to remember at the end of a line what was said at the
beginning of it, the imperfect marks will convey to you some sense of what
I long to say. We had heard of your illness through Miss Moore, and I was
therefore very glad to learn that you are now quite well; do not run too
many risks or make your happiness depend too much upon dangers, or the
hunting of them. Sometimes the very thinking of you, and what you may be
about, wearies me with fears, and then the cogitations pause and change,
but without giving me rest. I know that much of this depends upon my own
worn-out nature, and I do not know why I write it, save that when I write
to you I cannot help thinking it, and the thoughts stand in the way of
other matter.

'See what a strange desultory epistle I am writing to you, and yet I feel
so weary that I long to leave my desk and go to the couch.

'My dear wife and Jane desire their kindest remembrances: I hear them in
the next room:... I forget—but not you, my dear Tyndall, for I am

'Ever yours,

'M. Faraday.'

This weariness subsided when he relinquished his work, and I have a
cheerful letter from him, written in the autumn of 1865. But towards the
close of that year he had an attack of illness, from which he never
completely rallied. He continued to attend the Friday Evening Meetings,
but the advance of infirmity was apparent to us all. Complete rest became
finally essential to him, and he ceased to appear among us. There was no
pain in his decline to trouble the memory of those who loved him. Slowly
and peacefully he sank towards his final rest, and when it came, his death
was a falling asleep. In the fulness of his honours and of his age he
quitted us; the good fight fought, the work of duty—shall I not say
of glory?—done. The 'Jane' referred to in the foregoing letter is
Faraday's niece, Miss Jane Barnard, who with an affection raised almost to
religious devotion watched him and tended him to the end.

I saw Mr. Faraday for the first time on my return from Marburg in 1850. I
came to the Royal Institution, and sent up my card, with a copy of the
paper which Knoblauch and myself had just completed. He came down and
conversed with me for half an hour. I could not fail to remark the
wonderful play of intellect and kindly feeling exhibited by his
countenance. When he was in good health the question of his age would
never occur to you. In the light and laughter of his eyes you never
thought of his grey hairs. He was then on the point of publishing one of
his papers on Magnecrystallic action, and he had time to refer in a
flattering Note to the memoir I placed in his hands. I returned to
Germany, worked there for nearly another year, and in June, 1851, came
back finally from Berlin to England. Then, for the first time, and on my
way to the meeting of the British Association, at Ipswich, I met a man who
has since made his mark upon the intellect of his time; who has long been,
and who by the strong law of natural affinity must continue to be, a
brother to me. We were both without definite outlook at the time, needing
proper work, and only anxious to have it to perform. The chairs of Natural
History and of Physics being advertised as vacant in the University of
Toronto, we applied for them, he for the one, I for the other; but,
possibly guided by a prophetic instinct, the University authorities
declined having anything to do with either of us. If I remember aright, we
were equally unlucky elsewhere.

One of Faraday's earliest letters to me had reference to this Toronto
business, which he thought it unwise in me to neglect. But Toronto had its
own notions, and in 1853, at the instance of Dr. Bence Jones, and on the
recommendation of Faraday himself, a chair of Physics at the Royal
Institution was offered to me. I was tempted at the same time to go
elsewhere, but a strong attraction drew me to his side. Let me say that it
was mainly his and other friendships, precious to me beyond all
expression, that caused me to value my position here more highly than any
other that could be offered to me in this land. Nor is it for its honour,
though surely that is great, but for the strong personal ties that bind me
to it, that I now chiefly prize this place. You might not credit me were I
to tell you how lightly I value the honour of being Faraday's successor
compared with the honour of having been Faraday's friend. His friendship
was energy and inspiration; his 'mantle' is a burden almost too heavy to
be borne.

Sometimes during the last year of his life, by the permission or
invitation of Mrs. Faraday, I went up to his rooms to see him. The deep
radiance, which in his time of strength flashed with such extraordinary
power from his countenance, had subsided to a calm and kindly light, by
which my latest memory of him is warmed and illuminated. I knelt one day
beside him on the carpet and placed my hand upon his knee; he stroked it
affectionately, smiled, and murmured, in a low soft voice, the last words
that I remember as having been spoken to me by Michael Faraday.

It was my wish and aspiration to play the part of Schiller to this Goethe:
and he was at times so strong and joyful—his body so active, and his
intellect so clear—as to suggest to me the thought that he, like
Goethe, would see the younger man laid low. Destiny ruled otherwise, and
now he is but a memory to us all. Surely no memory could be more
beautiful. He was equally rich in mind and heart. The fairest traits of a
character sketched by Paul, found in him perfect illustration. For he was
'blameless, vigilant, sober, of good behaviour, apt to teach, not given to
filthy lucre.' He had not a trace of worldly ambition; he declared his
duty to his Sovereign by going to the levee once a year, but beyond this
he never sought contact with the great. The life of his spirit and of his
intellect was so full, that the things which men most strive after were
absolutely indifferent to him. 'Give me health and a day,' says the brave
Emerson, 'and I will make the pomp of emperors ridiculous.' In an eminent
degree Faraday could say the same. What to him was the splendour of a
palace compared with a thunderstorm upon Brighton Downs?—what among
all the appliances of royalty to compare with the setting sun? I refer to
a thunderstorm and a sunset, because these things excited a kind of
ecstasy in his mind, and to a mind open to such ecstasy the pomps and
pleasures of the world are usually of small account. Nature, not
education, rendered Faraday strong and refined. A favourite experiment of
his own was representative of himself. He loved to show that water in
crystallizing excluded all foreign ingredients, however intimately they
might be mixed with it. Out of acids, alkalis, or saline solutions, the
crystal came sweet and pure. By some such natural process in the formation
of this man, beauty and nobleness coalesced, to the exclusion of
everything vulgar and low. He did not learn his gentleness in the world,
for he withdrew himself from its culture; and still this land of England
contained no truer gentleman than he. Not half his greatness was
incorporate in his science, for science could not reveal the bravery and
delicacy of his heart.

But it is time that I should end these weak words, and lay my poor garland
on the grave of this

Just and faithful knight of God.

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